Biotin

What it is

Biotin (vitamin B7) is a water-soluble vitamin that helps enzymes build fats and break down amino acids. It is in eggs, nuts, legumes and some vegetables, and gut bacteria make some too, so dietary deficiency is rare. Cervantes 2025

The adequate intake for adults is about 30 micrograms a day. A balanced Western diet supplies roughly 35-70 micrograms, while hair, skin and nail products commonly contain 5-10 mg, more than 100 times as much. Yelich 2024

In the US it is sold as a dietary supplement with no efficacy review, and the FDA has issued safety communications about lab-test interference. In the EU, food supplements may carry the claim that biotin contributes to normal hair. That claim rests on deficiency harming hair; it does not mean extra biotin improves hair that is already normal.

How it works

In deficiency, whether inherited or acquired, biotin loss causes hair thinning, a rash around the eyes, nose and mouth, and later neurological symptoms. Giving biotin reverses the hair and skin signs. Cervantes 2025 Wolf 2026

Above sufficiency, no mechanism has been shown by which extra biotin boosts keratin or follicle activity. A review of 18 reported cases where biotin helped hair or nails found every one had an underlying cause such as deficiency, uncombable hair syndrome or brittle nail syndrome. Patel 2017

People who can become deficient include those with inherited biotinidase deficiency (caught by newborn screening), long-term users of anticonvulsants such as valproate, people on long-term antibiotics or intravenous feeding without biotin, and people who regularly eat raw egg whites, whose avidin binds biotin. Cooking inactivates avidin.

What the studies show

• A 1966 double-blind trial of 10 mg/day for 4 weeks in 46 women with diffuse hair loss found both groups improved with no difference between biotin and placebo (as summarised in a later review). Yelich 2024
• A systematic review of 3 studies concluded that the use of biotin as a hair supplement is not supported by high-quality studies. Yelich 2024
• In 10 healthy men, 14 days of 5 mg biotin did not change hair growth speed (2.50 to 2.47 mm/week, p = 0.53). Only biotin combined with minoxidil changed it significantly. The study was tiny and short. Valentim 2024
• In 156 women after sleeve gastrectomy, 72% had temporary hair loss. Self-reported improvement with 1 mg/day biotin was 23% in biotin-deficient women and 38% in non-deficient women, a difference that was not significant. Sen 2021
• In 60 acne patients on isotretinoin, those also taking 10 mg/day biotin for 4 months had more anagen and less telogen hair than at baseline. The study was open-label, not blinded. Aksac 2021
• A 6-week trial of two brands of weekly 5 mg biotin injections with dexpanthenol in 50 people improved hair counts in both, but with no placebo arm the result cannot be credited to biotin. Samadi 2022
• In 541 women with hair loss at one clinic, 38% had serum biotin under 100 ng/L. There was no control group, the assay was not stated and serum biotin swings widely day to day. The author still advised against routine biotin without proven deficiency. Trueb 2016
• In 90 women with chronic telogen effluvium versus 90 controls, serum and urine biotin did not differ. Durusu Turkoglu 2024
• In 60 men with pattern hair loss versus 60 controls, serum biotin was lower but not related to severity. Whether biotin helps was not tested. El-Esawy 2019

How it's used in studies

Hair studies used 1 mg/day after weight-loss surgery, 5 mg/day in healthy men, 10 mg/day in isotretinoin patients and 5 mg weekly by injection. Inherited biotinidase deficiency is treated with 5-10 mg/day for life. Wolf 2026

Side effects and safety

Lab-test interference is the main risk. Many blood tests use a biotin-streptavidin system. High blood biotin can make some assays read falsely high and others falsely low.

• In healthy adults taking 10 mg/day for 7 days, 9 of 23 biotin-based immunoassays gave wrong results, while none of 14 non-biotin assays did. Li 2017
• Thyroid tests can mimic Graves' disease, with high T4 and T3 and suppressed TSH, and normalize faster than thyroid hormone could change. Elston 2016 In 13 people taking 10 mg/day for 8 days, TSH, free T4 and total T3 shifted on one major platform and thyroglobulin read falsely low on another, peaking about 2 hours after a dose. Ylli 2021
• A falsely low troponin result can hide a heart attack. The FDA keeps a list of troponin assays still affected. FDA
• The problem is not rare: 7.7% of surveyed Mayo Clinic outpatients took biotin, and 7.4% of emergency-department blood samples carried biotin at or above one manufacturer's lowest interference threshold. Katzman 2018

Advice summarised in a 2024 review is to stop about 2 days before testing, up to a week after very high doses, and to tell your doctor and the lab either way. Yelich 2024 No direct toxicity is established at supplement doses. The practical risks are misdiagnosis and spending money while missing the actual cause of hair loss.

Bottom line

Biotin helps people with a documented deficiency, and a clinician should guide that. For everyone else, including pattern hair loss, telogen effluvium and "weak hair", the evidence says it will not help. For shedding, better first steps are a proper diagnosis and checking iron, thyroid, vitamin D and diet; see iron and ferritin, vitamin D, zinc and diet and hair. If you take it anyway, tell every clinician and lab and stop before blood tests. Discuss with a doctor.

Fun facts

• A hair vitamin can fake a thyroid disease. People taking megadose biotin have been misdiagnosed with Graves' disease, with results that normalized after stopping faster than thyroid hormone physically can. Elston 2016
• Raw egg white contains avidin, a protein that grips biotin tightly enough to cause deficiency. Cooking destroys it. Wolf 2026