Most hair loss in Crohn's disease is shedding rather than balding, it usually starts two to four months after the worst of a flare rather than during it, and in the great majority of cases it regrows. The pattern matters more than the amount: even thinning all over the scalp behaves very differently from smooth coin-shaped patches, and the two have different causes, different tests and different outcomes.
What the internet mostly offers is a list of possible culprits with no way to tell them apart. This article is built the other way round: start with the timing, then the pattern, then the bloods, then the drugs, and say plainly where the evidence for Crohn's specifically simply does not exist.
The short answer: this is usually telogen effluvium
The commonest kind of hair loss after a Crohn's flare is telogen effluvium, a diffuse non-scarring shedding triggered by a systemic event. Hair follicles that were happily growing get pushed into their resting phase early, all at roughly the same time, and then release together.
The single most useful fact about it is the delay. Diffuse shedding of resting hairs is seen three to four months after the triggering event, and an increase in shedding does not on its own tell you what the trigger was (Malkud 2015). That is why so many threads in r/CrohnsDisease describe hair coming out in handfuls at exactly the point where the diarrhoea has settled, the prednisolone is tapering and the person is finally eating again. It reads like a cruel joke. It is actually a lagging indicator.
Telogen effluvium is also, in the usual case, temporary. The Canadian expert algorithm on managing it is explicit that treatment consists of identifying triggers and correcting them, and it lists ordering appropriate investigations for metabolic abnormalities and nutritional deficiencies as part of the assessment. It also makes a point that will resonate with anyone who has had this dismissed: patients are frequently left alone with worry and helplessness while they wait for a dermatologist, and educating them is a crucial part of the treatment (Landells 2025).
There is a less reassuring variant. Chronic telogen effluvium is a diffuse shedding of the whole scalp with no obvious cause that runs a prolonged, fluctuating course over years. In the original series of 355 patients, almost all women aged 30 to 60, the onset was usually abrupt and the shedding severe enough that hair came out in handfuls, but the author's conclusion was that it represents shedding rather than true loss and does not cause complete baldness (Whiting 1996). That distinction, shedding versus loss, is the one worth holding on to.
Why the hair you lose was already committed months ago
Scalp hair does not grow continuously. Each follicle cycles through a long growing phase, a short transitional phase and a resting phase, and the hairs on your head are deliberately out of step with each other so that shedding is invisible. Telogen effluvium is what happens when that desynchronisation breaks and a large cohort of follicles enters the resting phase at once.
This is why working out the trigger is a calendar exercise. If you first noticed clumps in the shower in March, look at December and January, not at March. In Crohn's disease the December list is usually crowded: a flare, a course of steroids, a hospital admission, a surgical resection, a general anaesthetic, a fever, several kilograms of unintended weight loss, and a brand new immunosuppressant. Any one of those is a recognised trigger. Having four of them inside a month is unremarkable in Crohn's, and it is precisely why single-cause reasoning fails here.
There is a plausible mechanism for inflammation itself contributing, and it is worth stating carefully because it is often overstated. In cultured human hair follicles, interleukin-1 alpha, interleukin-1 beta and TNF-alpha were all potent inhibitors of follicle growth, producing distorted, poorly keratinised follicles that resembled the changes reported in alopecia areata (Philpott 1996). That is an in vitro study on isolated follicles, not a study of people with Crohn's disease, and it does not show that your CRP predicts your shedding. What it does show is that the cytokines that drive intestinal inflammation are capable of shutting hair growth down directly, which makes the timing observed in the clinic biologically sensible rather than coincidental.
Four different things get called "Crohn's hair loss"
The word people search for is one word. What arrives in a dermatology clinic is four or five separate conditions. Sorting them is the highest-value thing you can do before an appointment, because it changes which questions are worth asking.
| What it looks like | What it probably is | What tends to go with it | What it usually means |
|---|---|---|---|
| Even thinning all over, more hair in the shower and on the pillow, parting looks wider | Telogen effluvium | A flare, surgery, hospital stay, fever or rapid weight loss two to four months earlier | Usually self-limiting once the trigger is corrected |
| Smooth, round or oval bald patches, normal-looking skin underneath, sometimes eyebrows or lashes too | Alopecia areata | Other autoimmune conditions; more common in IBD than in the general population | Unpredictable course; has its own treatments and its own specialty |
| Sudden heavy loss within days to weeks of starting a drug, sometimes with low blood counts | Drug-related loss, including anagen effluvium | A new or newly increased medication; abnormal full blood count | A reason to contact your team promptly, not to stop the drug yourself |
| Scaly, crusty, itchy or bleeding patches, hair missing from those patches specifically | A scalp skin condition: psoriasis, seborrhoeic dermatitis, eczema, or a paradoxical drug reaction | Skin problems elsewhere; often flares alongside the gut | Needs a dermatologist; treating the scalp is what regrows the hair |
| Gradual thinning at the crown or a receding temporal hairline over years, no obvious trigger | Female or male pattern hair loss | Family history; age; menopause | Common, and frequently misattributed to Crohn's |
That last row deserves its own sentence, because it is the one people resist. Pattern hair loss is extremely common independent of any bowel disease. In 178 healthy postmenopausal women aged 50 to 65, assessed with standardised photography and trichoscopy by three dermatologists, the prevalence of female pattern hair loss was 52.2% (95% CI 44.6 to 59.8), and after adjustment only a body mass index of 25 or above remained significantly associated (Chaikittisilpa 2022). Those were women without IBD. If you are 55 and your crown has been slowly thinning for a decade, Crohn's may be a bystander.
Is hair loss actually more common in people with IBD? The numbers are a mess
There is a published association between inflammatory bowel disease and alopecia, and specifically alopecia areata. It is weaker and more confused than the way it gets quoted.
The main source is a 2021 systematic review that searched the literature from 1967 to 2020, included 79 studies in the review and pooled 19 of them. It reported a pooled prevalence of non-scarring alopecia among IBD patients of 1.12%, and a prevalence of IBD among people with scarring and non-scarring alopecia of 1.99%. It compared alopecia areata prevalence in IBD with the general population as 0.63% versus 0.1%, and IBD prevalence in the alopecia groups as 1.99% versus 0.396%, both differences reported as statistically significant. Its conclusion was that IBD and alopecia, particularly alopecia areata, appear to be strongly associated, and that dermatology patients with alopecia may benefit from screening for IBD (Maghfour 2021).
Two problems, and we could not resolve either from the abstract.
First, the arithmetic. The pooled prevalence of 1.12% is reported with a 95% confidence interval of 3.1 to 39.9, and the 1.99% figure with a confidence interval of 6.2 to 34. In both cases the interval does not contain the point estimate it is attached to, which cannot be right. Heterogeneity was also extreme, at 98.6% and 99%. We have printed the numbers as the paper reports them and we are telling you plainly that we could not reconcile them.
Second, the comparator. The paper uses 0.1% as general-population alopecia areata prevalence. The 2026 German S3 guideline reports population-based prevalence in Germany of 0.22% (95% CI 0.21 to 0.22) in 2016 and 0.21% (0.20 to 0.22) in 2020, with around 72 new diagnoses per 100,000 people in 2020, and notes that international data show a pooled prevalence of 2.1% with large regional differences (Blume-Peytavi 2026). Against 0.22% the IBD figure of 0.63% is still higher. Against a pooled international 2.1% it would be lower. Which comparator is appropriate is a real methodological question, and the direction of the headline finding depends on the answer.
A narrative review of alopecia areata in IBD reaches a similar place: the autoimmune mechanism of alopecia areata is thought to involve Th1 lymphocytes and proinflammatory cytokines including interferon gamma, TNF-alpha, interleukin-1 and interleukin-2, which overlap with the cytokines implicated in IBD, and alopecia areata is also described as an adverse effect of anti-TNF biological therapy (Sobolewska-Włodarczyk 2016). A separate 2025 case-control comparison of alopecia areata and inflammatory bowel disease also exists, but no abstract is available for it through PubMed or Europe PMC and we were not able to read it, so we cite it only for the fact that it exists rather than for anything it concludes. Its declarations state that the research was supported in whole or in part by HCA Healthcare or an affiliated entity, and that the authors declare no competing interests (Kooner 2025).
The nutrition question, and the ferritin trap that catches almost everyone
Iron, zinc and protein status all matter for hair, and all three are commonly disturbed in Crohn's disease. The specific trap is that the blood test most people rely on is the one most distorted by the disease.
Anaemia first. In an individual patient data meta-analysis of 2,192 European IBD patients, the overall prevalence of anaemia was 24% (95% CI 18 to 31), and 27% (19 to 35) in Crohn's disease specifically compared with 21% (15 to 27) in ulcerative colitis. Fifty-seven per cent of the anaemic patients were iron deficient. Active disease more than doubled the odds of anaemia (odds ratio 2.72), and the patients were mainly treated in tertiary referral centres, so this is a sicker-than-average sample (Filmann 2014).
Now the trap. Ferritin is an acute-phase protein: it goes up when you are inflamed, for reasons that have nothing to do with how much iron you have available. The European consensus on iron deficiency and anaemia in IBD therefore uses different thresholds depending on inflammation, with a serum ferritin below 30 micrograms per litre taken as iron deficiency in patients without clinical, endoscopic or biochemical evidence of active disease, and a threshold below 100 micrograms per litre used in the presence of inflammation (Dignass 2015). Your laboratory's reference range does not know you have Crohn's. This is why, in hair loss threads on r/CrohnsDisease, the most practically useful comment is invariably someone asking what the person's ferritin actually is and pointing out that the IBD threshold is higher than the lab's. That is a community shortcut to a real guideline, and the action it implies is to request the ferritin and the CRP in the same blood draw and have your IBD team read them together.
How strong is the iron-to-hair link itself? Weaker than the supplement aisle implies, and mostly studied outside IBD. A 2026 systematic review and meta-analysis of serum trace elements in telogen effluvium pooled 29 articles and found significantly lower serum ferritin in cases than controls, with a standardised mean difference of -0.57 (95% CI -1.01 to -0.12, p = 0.01), and lower vitamin D, standardised mean difference -0.87 (-1.49 to -0.25, p = 0.006). Heterogeneity was high and the populations were predominantly female (Ahmed 2026). A cross-sectional study of 100 women, 50 with telogen effluvium and 50 controls, found mean ferritin of 24.3 versus 44.8 nanograms per millilitre, with ferritin below 15 in 28% of cases and none of the controls (Thamotharan 2025). And in a retrospective review of 210 patients with pattern hair loss and 210 matched controls, ferritin was lower in women with female pattern hair loss, most markedly in premenopausal women, leading the authors to suggest iron screening for hair loss patients (Park 2013).
Read those three together and the honest summary is: low ferritin travels with hair shedding, consistently, in studies of women without inflammatory bowel disease, and none of them randomised anyone to iron replacement and measured hair. Association is a reason to check and correct a deficiency you have. It is not proof that correcting it will regrow your hair.
Beyond iron. Micronutrient deficiency is common in Crohn's and often unmeasured. In 182 patients diagnosed within the previous 18 months, 36% met criteria for malnutrition, and among the 135 who had at least one micronutrient checked, 78% had at least one deficiency; prior surgery, active Crohn's disease and diarrhoea all raised the odds (Gold 2023). A multicentre cross-sectional study of 295 IBD patients found disease-related malnutrition in 23% with no significant difference between Crohn's and ulcerative colitis, and at least one micronutrient deficiency in 23% (Viganò 2024). A more recent population-based Swedish study of 306 outpatients found a lower figure, 11.8% (95% CI 8.2 to 15.4) by GLIM criteria, with malnutrition significantly more common in women than men, 16.9% versus 7.0%, and independently associated with disease activity in the previous year (Korwel 2026). The spread from 11.8% to 36% is mostly about setting and definition: recently diagnosed hospital-referred patients are not the same population as stable outpatients, and GLIM is not the same yardstick as the older ESPEN definition. Note also that none of these definitions is a weight check: you can be overweight with Crohn's disease and undernourished at the same time, which is why a normal BMI is not a reason to skip micronutrient testing when your hair is shedding.
Zinc gets raised constantly in hair threads and deserves a precise statement. In 773 Crohn's and 223 ulcerative colitis patients with repeated measurements, zinc deficiency was associated with more subsequent hospitalisations, surgeries and disease-related complications, and normalising zinc was associated with improvement in those outcomes (Siva 2017). Note carefully what that study measured: hospitalisations and surgery, not hair. It is a strong reason to have zinc checked and corrected if low. It is not evidence that zinc supplements grow hair.
Other deficiencies are routinely missed because nobody looks. In a retrospective review of 611 hospitalised IBD patients, copper had been measured in 12.3%, vitamin A in 10.1%, vitamin E in 10.3% and vitamin K in 4.6%. Among Crohn's patients who were tested, 25.4% were copper deficient, 53.3% vitamin A deficient, 23.7% vitamin E deficient and 29.4% vitamin K deficient. Those percentages are of the small tested subgroup, not of all 611, which is exactly why the authors conclude these deficiencies are underrecognised rather than that half of all Crohn's patients are vitamin A deficient (Kamel 2024). A dermatology-facing review of the same territory notes that dermatologists may be the first to identify an undiagnosed micronutrient deficiency in IBD, and that monitoring and repletion are affected by disease activity and by interactions with IBD medication (Le 2024).
Blood tests worth asking about, and what a normal result does not rule out
This is not a self-testing protocol. It is a list to bring to the person who orders your bloods, so that one request covers the ground instead of three.
| Test | Why it is on the list | What a normal result does not rule out |
|---|---|---|
| Full blood count | Anaemia; also low white cells or platelets, which matter urgently on a thiopurine | Iron deficiency without anaemia, which is far more common |
| Ferritin, requested with CRP | The core iron store measure, and the CRP is what makes it interpretable | Deficiency, if read against the lab range rather than the IBD threshold |
| Transferrin saturation | Less distorted by inflammation than ferritin alone | Nothing much; it is a useful cross-check |
| Vitamin B12 and folate | Absorption sites are in the small bowel, which is where Crohn's often is | Functional deficiency with a borderline result |
| Zinc | Commonly low in IBD and linked to worse disease outcomes | Much: serum zinc is an imperfect marker of body stores |
| Thyroid function | Both under- and overactive thyroid cause diffuse shedding | Early autoimmune thyroid disease with normal hormones |
| Coeliac serology, if not already done | Coeliac disease is associated with alopecia areata and can coexist with IBD | Coeliac disease if you are already avoiding gluten |
| Vitamin D | Lower in telogen effluvium cases than controls in the pooled data | Any causal role; the evidence here is associational |
The reason to ask for these together is bluntly practical: each separate appointment costs you weeks, and the hair you are worried about is on a three-month feedback loop. Our guide on how to prepare for a GI doctor appointment covers how to get a request list onto the record in a short slot, and questions to ask your doctor about Crohn's disease covers phrasing that tends to get answered rather than deflected.
Medication: which drugs are genuinely implicated, and which are folklore
Some drugs used in Crohn's disease really do cause hair loss. The forums over-attribute it, and the literature under-documents it, which is an unhelpful combination.
Thiopurines. Azathioprine and mercaptopurine are the drugs most often named in Crohn's hair loss threads, and hair loss is a recognised adverse effect. The severe version travels with bone marrow suppression. In one reported case, a teenager developed hair loss, pancytopenia, bloody diarrhoea and fever shortly after starting azathioprine; pharmacogenetic testing found compound heterozygosity of the NUDT15 gene, and she recovered fully after the drug was stopped (Hsu 2022). That is a single case report and the underlying condition was myasthenia gravis, not Crohn's, so it tells you about the drug rather than about the disease. The clinically important part is the pairing: heavy hair loss plus a new infection, mouth ulcers, bruising or feeling wiped out on a thiopurine is a blood-count question, and it needs a same-week call to your IBD team rather than a decision made at home.
Anti-TNF drugs. Here the picture genuinely splits. On one side, there are case series. Five new cases of alopecia areata developing during anti-TNF therapy were reported alongside a review of eleven previously published ones; a third of the cases had a personal or family history of alopecia areata, most presented with rapid extensive loss, the prognosis was generally poor, and where the anti-TNF was continued the course did not appear to change (Ferran 2011). A more recent case series describes psoriasiform alopecia areata-like reactions secondary to anti-TNF therapy, which may appear acutely or be delayed by months to years, and argues that recognising them histopathologically matters precisely so that therapy is not discontinued inappropriately (Liu 2025).
On the other side is the only IBD-specific comparison we found. A retrospective multicentre case-control study identified 58 people who developed alopecia areata after an IBD diagnosis and 90 contemporaneously treated controls who never did. Anti-TNF use was significantly more common in the cases, 40.7% versus 20.0% (p = 0.006). Three further findings are worth as much as that one:
- The majority of cases had endoscopic remission or mild disease activity at the time their alopecia areata was diagnosed. So the hair loss was not a marker of active bowel inflammation.
- There was no difference in partial or complete improvement of the alopecia between people who stopped their IBD therapy and those who continued it (p = 0.57).
- Severity predicted outcome: nobody with severe alopecia areata achieved complete improvement, versus 33.3% of those with non-severe disease, and any improvement occurred in 50% versus 84.9% (Pan 2024).
Read that second point twice, because it is the most decision-relevant sentence in this article. In the only IBD series to ask the question, stopping the IBD drug did not make the hair come back.
The control-arm problem, worked through. A 2025 systematic review and meta-analysis of paradoxical psoriasis in children with IBD on anti-TNF drugs pooled 13 studies and reported an incidence of 6.8% (95% CI 0.04 to 0.10), with 255 of 3,349 children (7.6%) affected across all included studies and a median time to eruption of 15 months. Infliximab accounted for 151 cases and adalimumab for 40 (Gaston 2025). Note that the denominators shift through that abstract: 3,349 children, 255 affected, but the drug attribution adds up to 191 and the management figures are reported out of 229. We could not reconcile which subgroup each percentage belongs to.
More importantly, 6.8% is a single-arm incidence with no comparison group, and the background rate of psoriasis in children with IBD not on anti-TNF is not zero. When a meta-analysis did make that comparison in an adult IBD population across 14 studies, there was no significant difference in psoriasis development between anti-TNF-treated and anti-TNF-naive patients (relative risk 1.14, 95% CI 0.77 to 1.68), no difference between Crohn's and ulcerative colitis, and no difference by agent (Jun 2022). Those are different populations, children versus adults, so this is not a direct contradiction. But it is the reason to be careful: a headline percentage from a single arm and a null result from a controlled comparison are telling you different things, and only the second one estimates an effect.
The pharmacovigilance view, with its limits. An analysis of 181,838 reports of drug-associated alopecia in the FDA Adverse Event Reporting System from 2004 to 2024 identified 64 drugs with significant signals. Oncology drugs dominated at 37.5% of reports, with immune system medications at 10.9%. Time to onset was bimodal: 40.2% of cases within 30 days and 13.1% at 240 to 360 days, with a significantly shorter latency in men than women, 108 days versus 236. And 23.4% of the high-signal drugs did not mention alopecia in their US prescribing information (Li 2025). Spontaneous reporting databases cannot give you a rate, because there is no denominator and reporting is driven by publicity as much as by biology. What this is good for is the last finding: if your drug's leaflet does not list hair loss, that is not evidence it never happens. A systematic review specifically of drug-induced alopecia areata has also been published, though it is a short research letter with no abstract available and we could not read it, so we cite it only for its existence (Ezemma 2024); its authors declared no conflicts of interest.
The strange part: some drugs used for IBD also treat hair loss
This is where the story turns, and it is worth knowing before an appointment because it changes what a referral can offer.
Alopecia areata now has licensed treatment, and it comes from the same pharmacological family that treats inflammatory bowel disease. Two randomised placebo-controlled phase 3 trials enrolled 654 and 546 adults with severe alopecia areata, defined as at least 50% scalp hair loss. At week 36, the percentage reaching a Severity of Alopecia Tool score of 20 or less was 38.8% on baricitinib 4 mg, 22.8% on 2 mg and 6.2% on placebo in the first trial, and 35.9%, 19.4% and 3.3% in the second (King 2022).
Do the subtraction, because the 38.8% figure is the one that gets quoted. The difference from placebo was 32.6 percentage points (95% CI 25.6 to 39.5) in both trials for the 4 mg dose, and around 16 points for the 2 mg dose. So the drug-specific gain is roughly a third of patients, not two fifths, and the placebo arm regrew hair in 3% to 6% of cases, which is itself informative about the natural course. Secondary outcomes favoured the 4 mg dose but generally not the 2 mg dose. Acne, raised creatine kinase and raised cholesterol were more common on the drug. The trials were funded by Eli Lilly under licence from Incyte, which is the manufacturer of the drug being tested.
The longer-term safety data from the same programme, covering 1,303 patients and 2,789.7 patient-years with a maximum exposure of four years, reported low rates of serious adverse events (incidence rate 2.6 per 100 patient-years) and discontinuations (1.7), herpes zoster at 1.9, and no deaths in either study (King 2025). Several authors of that paper are employees of the manufacturer, and the rest report consulting or investigator relationships with it.
The overlap with IBD is direct. A case report titled "Gut instinct" describes using tofacitinib, a JAK inhibitor used in ulcerative colitis, to treat alopecia areata in someone who also had inflammatory bowel disease (Peterson 2021). If you have Crohn's disease and severe alopecia areata, there is at least a conversation to be had between gastroenterology and dermatology about whether one drug can be asked to do two jobs. That is a specialist conversation, not a request to make at a pharmacy counter, and JAK inhibitors are not licensed across all of IBD.
One more trial deserves a mention, with a warning attached. A double-blind randomised controlled trial in Peshawar, Pakistan, compared tofacitinib with azathioprine in 104 patients aged 12 and over with at least 50% scalp hair loss present for six years or more. Mean Severity of Alopecia Tool scores fell from about 91 in both groups to 14.1 on tofacitinib and 63.9 on azathioprine at six months (Paracha 2024). The abstract then reports that difference as "11.5 points; 95% confidence interval, 38.3-61.3", and those two figures are not compatible: the confidence interval does not contain 11.5, while it does bracket the roughly 50-point gap implied by the group means. We could not reconcile the stated point estimate with the stated interval and we are not going to pick the more flattering reading. Two other things about that trial: the population had extremely long-standing, severe disease and a mean age of around 21, which is not the typical middle-aged Crohn's patient shedding hair after a flare; and the azathioprine arm also improved substantially, which is a curiosity given that azathioprine appears earlier in this article as a suspected cause of hair loss. Both things can be true. A drug that suppresses an autoimmune attack on follicles can also, in some people, poison follicles directly.
Clairop logs meals, symptoms and stool in seconds, then looks for the foods your gut reacts to, including reactions that land days later.
What else to rule out, including two places where the evidence disagrees with itself
Thyroid. Both underactive and overactive thyroid cause diffuse hair shedding, and thyroid function should be on the blood request. Whether people with IBD get more thyroid disease is genuinely unsettled. A 2025 review states that patients with Crohn's disease and ulcerative colitis exhibit a higher prevalence of thyroid disorders than the general population, while also concluding that current data do not show a unanimous association between Graves' disease or Hashimoto's thyroiditis and chronic IBD (Calcaterra 2025). A retrospective case-control study of 313 IBD patients and 833 people having screening colonoscopy found the opposite direction: clinically relevant thyroid disorders were less common in IBD, 8.3% versus 12.9% (p = 0.029), and after adjustment the odds ratio for IBD was 0.51 (95% CI 0.34 to 0.76), with the authors concluding that routine thyroid testing in the absence of symptoms seems unnecessary, at least in their region (Dore 2021). We cannot settle that from here. The practical read is that thyroid testing is justified by the hair loss itself, which is a symptom, rather than by your IBD diagnosis.
Coeliac disease. This one is cleaner in direction and more limited in what it implies. In a nationwide case-control study of 33,401 people with alopecia areata and 66,802 matched controls, coeliac disease prevalence was twice as high in the alopecia group, 1.1% versus 0.6%, odds ratio 1.95 (95% CI 1.69 to 2.25), with the highest risk in those aged 40 and over (Wohl 2025). That is a reason to have coeliac serology checked if it has never been done, especially with patchy hair loss. It is not a reason to expect a diet to fix the hair. In five patients who had both coeliac disease and alopecia areata, a gluten-free diet resolved the coeliac disease clinically, serologically and histologically, and had no effect at all on the course of the alopecia (Bardella 2000). Five patients is a tiny study, and older case reports point the other way, but it is the most directly relevant experiment anyone has published and it was negative.
Scalp disease that gets mistaken for Crohn's hair loss
A recurring pattern in r/CrohnsDisease hair threads is someone describing crusty, scaly or bleeding patches on the scalp, assuming the hair loss is "the Crohn's", and being told by several commenters to see a dermatologist. They are right, and the reason is specific: hair missing from visibly inflamed skin is a different problem from hair falling evenly out of healthy skin.
Scalp psoriasis, seborrhoeic dermatitis and eczema can all cause hair loss over affected areas, and skin conditions in general are more common in people with IBD. Paradoxical psoriasis during anti-TNF treatment adds another route to the same appearance, and the scalp is one of its typical sites (Gaston 2025). The distinction that matters most is scarring versus non-scarring. Telogen effluvium and alopecia areata are non-scarring: the follicle survives and can regrow. Some inflammatory scalp conditions, if left untreated long enough, are not. That is the single best argument for getting a dermatologist to look rather than waiting to see whether it settles, and it is why "treat the scalp" often turns out to be the thing that regrows the hair.
A dermatologist has tools your IBD team does not. Trichoscopy, a magnified look at the scalp, distinguishes patterns that are invisible to the naked eye, and the pull test gives a same-day, objective read on whether you are actively shedding. Updated guidance based on 181 participants lowered the normal cutoff for the pull test to two hairs or fewer per pull, found no significant difference between Caucasian, Asian and Afro-textured hair, and removed the traditional five-day washing restriction beforehand (McDonald 2017). That last detail is useful if you have been told not to wash your hair before an appointment: the evidence does not support it.
Supplements: what the evidence supports, and how they can go wrong
Every hair loss thread produces the same three suggestions. Here is what each is worth, stated plainly, and we are not recommending that anyone start, stop or change a supplement.
Biotin. This is the one people are most confident about and the evidence is the weakest. A 2024 review searched for studies of oral biotin for hair growth or quality and found three that met its criteria. The highest-quality one was double-blind and placebo-controlled, and found no difference between biotin and placebo for hair growth. The other two looked at specific populations, people on isotretinoin and women after sleeve gastrectomy, were susceptible to multiple biases, and had no striking results in biotin's favour. The authors' conclusion was that there is a large discrepancy between public perception and the scientific literature (Yelich 2024).
There is also a concrete harm, and it is one that matters more for people with Crohn's than for the general public because you have far more blood tests. Biotin interferes with immunoassays that use biotin-streptavidin chemistry. In a study of 78 patients and controlled spike-in experiments, biotin caused false-low thyroglobulin and alpha-fetoprotein results and false-high anti-thyroglobulin and free thyroxine results with older reagents, with newer reagents tolerating higher concentrations, and tolerance differing between analyser manufacturers (Chiu 2025). A false thyroid result is exactly the wrong thing to acquire while being investigated for hair loss. If you take biotin, say so before bloods are taken.
Selenium. The reason not to freelance with trace elements is an American public health investigation. A misformulated liquid dietary supplement containing 200 times its labelled selenium concentration produced 201 cases of acute selenium toxicity across 10 states. The median estimated dose was 41,749 micrograms a day against a recommended dietary allowance of 55 micrograms. Frequently reported symptoms were diarrhoea in 78%, fatigue in 75% and hair loss in 72%, and at 90 days or beyond, 29% still had hair loss (MacFarquhar 2010). Selenium excess causes the symptom people take supplements to prevent.
Fat-soluble vitamins. A common misconception is that vitamins are safe and that more is better; hypervitaminosis of vitamins A, D, E, niacin and biotin can produce harmful skin effects (Chen 2026). This is not a general argument against supplements. It is an argument for testing before topping up, which is the opposite of what most hair-loss advice suggests.
How long until it grows back, and what "grown back" will look like
Telogen effluvium is described in the dermatology literature as self-limiting, with treatment consisting of identifying and correcting the trigger (Landells 2025), and chronic telogen effluvium, while it fluctuates for years, does not cause complete baldness (Whiting 1996). So the honest answer to "will it grow back" is: for the shedding kind, usually yes.
The honest answer to "how long" is that nobody has published a regrowth timeline for Crohn's disease specifically, so any page giving you a confident number for IBD made it up. What can be said is structural. Shedding stops before density returns, because those are two different events: the follicles have to finish resting and re-enter growth before there is anything new to see. Scalp hair grows in the region of a centimetre a month, so new growth becomes visible as a fringe of short hairs at the parting and hairline first, then takes many months to reach a length that blends in. That awkward halo of short regrowth is a good sign being mistaken for a bad one, and it is described repeatedly in the Crohn's threads.
Community accounts, which we are labelling as lived experience rather than evidence, mostly follow that arc: heavy loss during and after a bad period, a long flat stretch, then gradual recovery as disease control improves, sometimes with a changed texture. Several people in the thread that seeded this article describe more than one cycle, each tracking a hospital admission. One describes terrible loss for the first five to ten years after diagnosis and good hair thirty years in (r/CrohnsDisease thread). None of that is a prognosis. It is a reason not to treat month three as the final result.
Alopecia areata is different and less predictable. In the IBD series, severity at diagnosis was the significant predictor of resolution, with nobody in the severe group achieving complete improvement, and outcomes did not depend on whether IBD therapy was continued (Pan 2024). That is a reason to get patchy loss assessed early rather than to wait, because the treatment landscape for it has changed in the last few years.
What to track, so the timeline is actually visible
The whole problem with hair loss is that the cause sits three months upstream of the symptom, and nobody remembers three months back accurately. Four things make the connection legible:
- A dated shedding record, not an adjective. A count is not necessary; a daily note of light, moderate or heavy, plus "handfuls in the shower" when that happens, is enough to show a clinician a curve instead of a feeling.
- A monthly photo, standardised. Same room, same light, same parting, dry hair, front and crown. Month-to-month change is invisible to memory and obvious in a photo series. This is the single highest-value thing you can do.
- A timeline of events, kept alongside the symptoms. Flare start and end, hospital admissions, surgery, steroid courses, every drug start, stop and dose change, weight, and the dates of blood tests with the ferritin, CRP and zinc results written next to them. This is what turns "my hair is falling out" into "the shedding began eleven weeks after the admission in January".
- Whether the scalp itself is involved. Itch, flaking, soreness, bleeding, and whether the bald areas have normal skin or abnormal skin. That one observation routes you to the right specialist.
If you already track symptoms for your gut, this rides along: a hair note and a monthly photo attached to the same timeline as your flare dates, drug changes and test results means the three-month offset becomes visible instead of theoretical. Clairop keeps one dated record of symptoms, medication and food and produces a report you can take to an appointment, and you can see how it works if that is useful. The tracking does not treat anything. What it does is make a delayed pattern arguable in a ten-minute slot.
A worked example: two timelines that look identical for six weeks
Two people, both with ileal Crohn's, both first notice heavy shedding in the same week of April.
Person A. Admitted in late January with a flare, lost five kilograms, had a course of intravenous steroids, started azathioprine in February. Hair loss noticed mid-April, even across the whole scalp, more in the shower and on the pillow, no bald patches, scalp looks and feels normal. Ferritin 38 with CRP 22. Full blood count normal.
The interval from admission to shedding is about eleven weeks, squarely inside the expected three-to-four-month window for a systemic trigger (Malkud 2015). The ferritin of 38 would be reported in range by most laboratories and counts as iron deficiency under the IBD threshold of 100 with inflammation present (Dignass 2015). Azathioprine is a genuine candidate too, and there is no test that separates "the flare and hospital stay did it" from "the azathioprine did it" when they are eight weeks apart. The plan that follows is iron status corrected with the IBD team, blood counts monitored on the thiopurine, and a photo series started, with a review at three months rather than a decision now.
Person B. Same April onset. But the loss is two smooth circular patches behind the left ear, each the size of a two-pound coin, with completely normal skin inside them, and the eyebrows have thinned at the outer edges. Last colonoscopy showed healing, calprotectin is low, no admission, no new drugs for two years.
That is not telogen effluvium and the calendar exercise does not apply. Patchy, well-demarcated, non-scarring loss with eyebrow involvement and quiet bowel disease fits alopecia areata, which in the IBD series was typically diagnosed while the bowel was in endoscopic remission or only mildly active (Pan 2024). Person B needs dermatology, not a ferritin recheck, and needs it sooner rather than later because severity at presentation predicted the outcome in that series.
Same month, same complaint, entirely different article. This is why the pattern question comes before every other question.
Myths worth retiring
"Hair loss means my Crohn's is active." Not reliably. In the only IBD case-control series of alopecia areata, most patients were in endoscopic remission or had only mild activity when the hair loss was diagnosed (Pan 2024). And for the shedding kind the timing is retrospective by design: it reflects something that happened a season ago. If you want to know whether your disease is active, that is a separate question with separate tools, and how to tell if you are in a Crohn's flare covers them.
"It is definitely the biologic." It might be, and case series describe both alopecia areata and psoriasis-like scalp reactions on anti-TNF drugs (Ferran 2011, Liu 2025). But the meta-analysis that compared anti-TNF-treated IBD patients with anti-TNF-naive ones found no significant difference in psoriasis development, relative risk 1.14 (95% CI 0.77 to 1.68) (Jun 2022). A confidence interval spanning 1 is not evidence of an effect.
"Stopping the drug will bring it back." In the IBD series that asked, there was no difference in alopecia improvement between people who stopped their IBD therapy and those who continued (Pan 2024).
"Biotin fixes it." The best-designed study of biotin for hair growth found no difference from placebo, and there are only three studies in total (Yelich 2024). It can also skew your thyroid results (Chiu 2025), which is worth knowing when you are being investigated.
"My ferritin is normal, so iron is not the issue." Ferritin rises with inflammation, and European IBD guidance uses a threshold below 100 micrograms per litre when inflammation is present rather than the usual laboratory cutoff (Dignass 2015). A "normal" ferritin with a raised CRP is not reassurance.
"A gluten-free diet will regrow my hair." Coeliac disease is genuinely more common in people with alopecia areata (Wohl 2025), which is a reason to test for it. But in the five patients who had both and went gluten free, the coeliac disease resolved and the alopecia did not change at all (Bardella 2000).
"More supplements must help." Selenium excess causes hair loss: in the American selenium poisoning outbreak, 72% of 201 affected people reported it, and 29% still had it at 90 days (MacFarquhar 2010). Hypervitaminosis of several vitamins has skin consequences of its own (Chen 2026).
"Crohn's hair loss is permanent." Telogen effluvium is described as self-limiting once the trigger is corrected, and even the chronic fluctuating form does not cause complete baldness (Whiting 1996, Landells 2025). Alopecia areata is less predictable, but it now has licensed treatment that did not exist a few years ago (King 2022).
When to see a doctor promptly
Hair loss itself is rarely an emergency. What it sometimes sits next to is.
See a doctor promptly if you have: blood in your stool, unexplained weight loss, fever, night-time symptoms that wake you, symptoms of anaemia such as breathlessness, dizziness or a racing heart, mouth ulcers with a sore throat or unusual bruising while on a thiopurine or methotrexate, new bowel symptoms starting after the age of 50, or a family history of bowel cancer or IBD alongside new symptoms.
Contact your IBD team within days if: the hair loss started within weeks of a new or increased medication, especially a thiopurine; you have heavy loss plus any sign of infection; or the hair loss arrived alongside a return of gut symptoms.
Ask for a dermatology referral if: the loss is patchy rather than diffuse, your eyebrows or eyelashes are involved, the scalp itself is scaly, sore or bleeding, or diffuse shedding has continued for more than six months without improvement. Scarring and non-scarring hair loss have different outcomes, and telling them apart is a job for someone who can look at the scalp under magnification.
The honest bottom line
If your hair started falling out after a Crohn's flare, a hospital stay, surgery or a stretch of weight loss, the most likely explanation is telogen effluvium, the timing will point two to four months back rather than at last week, and the usual outcome is regrowth once the trigger has passed (Malkud 2015, Landells 2025). Get your iron status read against the IBD threshold rather than the laboratory range (Dignass 2015), get zinc, B12, folate, thyroid and coeliac status checked once rather than one at a time, and start a monthly photo so that month five has something to compare itself to.
If the loss is patchy with normal skin, treat that as a different condition and ask for dermatology early, because severity at presentation predicted outcome in the only IBD series that measured it (Pan 2024) and because effective treatment now exists (King 2022). If the scalp itself is inflamed, the hair follows the skin, and the skin is the thing to treat.
Three things we cannot tell you, and no page should pretend otherwise. Nobody has measured how common shedding is in Crohn's disease, because the only pooled prevalence figures come from coded alopecia diagnoses in a paper whose own confidence intervals do not contain its own point estimates (Maghfour 2021). Nobody has published a regrowth timeline for IBD specifically. And when a flare, a steroid course, a weight loss and a new drug all land in the same eight weeks, no test will apportion blame between them. What you can do is fix the deficiencies that are fixable, keep the disease control you have, give the follicles the three months they need, and stop judging the result at week four.
If the exhaustion is as bad as the hair, Crohn's fatigue in remission covers what is worth checking and what each result would explain, and how to explain Crohn's fatigue to people covers the conversation with the people who keep telling you it is just hair.
