Hair growth vitamins and biotin: what helps, what doesn't and when to see a GP

Why hair falls out

Losing 50–100 hairs a day is normal: old hairs fall out and new ones grow. It’s worth looking into if you’re finding much more hair on your brush and pillow, you notice bald patches, or your hair looks noticeably thinner.

According to the NHS, temporary hair loss is most often caused by:

• an illness;
• stress;
• weight loss;
• cancer treatment;
• iron deficiency.

Some causes can’t be fixed with vitamins. Male and female pattern hair loss is permanent and usually runs in families. Dry hair and hair loss can be signs of an underactive thyroid. Hormonal changes affect hair growth too, and they need a GP, not a hair gummy.

When hair vitamins help

Hair follicles need vitamins and minerals because their cells divide very fast. That’s why a deficiency can show up as hair loss. A 2019 review of vitamins and minerals in hair loss concluded that deficiencies are a modifiable risk factor, but there’s no proof supplements help when you’re not deficient.

The rule is simple: find the deficiency, then correct that one thing. A “hair, skin and nails” formula with a dozen ingredients doesn’t replace a blood test. It often contains lots of biotin and no iron at all.

Biotin for hair: what we know

Biotin (vitamin B7) helps your body use fats, carbohydrates and protein. Adults need 30 mcg a day, or 35 mcg when breastfeeding. Severe deficiency has never been reported in healthy people eating a normal mixed diet.

Your risk of running low is higher in these situations:

• Inherited biotinidase deficiency. Newborns are screened for it.
• Long-term heavy drinking.
• Pregnancy and breastfeeding: at least a third of pregnant women develop marginal deficiency.
• Some epilepsy medicines (carbamazepine, phenytoin, phenobarbital).
• Regularly eating raw egg whites.

Now to hair. A 2017 review found 18 reported cases where biotin helped hair or nails. Every one of those people had an underlying cause: biotin deficiency or a rare condition. There are no studies showing biotin improves hair in healthy people. NIH ODS describes the evidence as case reports and small studies at best.

Yet hair growth supplements typically contain 5,000–10,000 mcg of biotin. No upper limit has been set because toxicity hasn’t been seen in humans.

The real problem with big doses isn’t toxicity. It’s your blood test results.

Biotin and blood tests: the FDA warning

Many lab tests use a biotin–streptavidin reaction. High biotin levels in your blood from supplements can make results falsely high or falsely low.

The FDA issued a safety warning in 2017 and updated it in 2019. It followed the death of a patient on high-dose biotin whose troponin test (used to diagnose heart attacks) came back falsely low. Biotin can also distort thyroid tests and suggest an overactive thyroid that isn’t there.

What to do:

• Before any blood test, tell your GP and the lab that you take biotin, including in a multivitamin.
• Don’t assume stopping for a few hours is enough. The FDA says it isn’t known how long to wait. A single 10 mg dose has interfered with tests within 24 hours.
• If a result doesn’t match how you feel, remind your doctor about biotin.

Iron, zinc and other nutrients for hair

• Iron. The most common fixable cause on the NHS list. The decision rests on ferritin and a full blood count; see our guide to ferritin levels and iron deficiency. Don’t take iron without a test: too much is harmful.
• Zinc. You may fall short on a diet without meat or seafood. EFSA’s upper limit is 25 mg a day including food; our zinc guide shows how to stay under it.
• Vitamin D. Its role in hair growth is being studied, but there’s little evidence that supplements help hair. Follow the general UK advice in our vitamin D3 guide.
• Selenium. Here the risk is too much: the main signs of chronic selenium toxicity are hair loss and brittle nails. EFSA’s upper limit is 255 mcg a day.

When to see a GP or dermatologist

The NHS advises seeing a GP if you’re worried about hair loss, and finding out the cause before paying for a commercial hair clinic. Your GP can order ferritin, a full blood count and a thyroid test, and refer you to a dermatologist if needed. Don’t put it off in these cases:

• You have round bald patches, or hair is coming out in clumps.
• Your scalp is itchy, sore, flaky or red.
• You also feel tired, cold or constipated, or have gained weight. These can be signs of an underactive thyroid.
• Your periods have become heavier or irregular.
• The hair loss started after a new medicine.
• A child is losing hair.

What treats hair loss when vitamins won’t

According to the NHS, most hair loss doesn’t need treatment. It’s either temporary and will grow back, or a normal part of getting older. Hair loss caused by a medical condition usually stops or grows back once you’ve recovered.

If hair loss is getting you down, your GP can talk you through the options:

• minoxidil – a main treatment for male pattern baldness, also used for female pattern hair loss;
• finasteride – for men only; women should not use it;
• steroid injections or creams – for bald patches;
• a hair transplant – for permanent hair loss.

No treatment works for everyone. Minoxidil and finasteride only work for as long as you use them, and not all treatments are available on the NHS. So start with a GP or dermatologist, not a random course of supplements.

Hair, skin and nails formulas: what to check

If you still want a formula, pick up the bottle and find these lines on the label:

• Biotin. 5,000–10,000 mcg is 160–330 times the daily need. It won’t help hair without a deficiency, and it skews blood tests.
• Zinc. Look for 10–15 mg at most: food adds about 8–12 mg, and the limit is 25 mg.
• Selenium. Add it up across all your products: too much itself causes hair loss.
• Vitamin A as retinol. It has a low upper limit and carries risks in pregnancy. More in our guide to vitamins A and E.
• Collagen, keratin, herbal extracts. Doses are usually small, and there’s little or no evidence they help hair. On collagen, see collagen supplements.

Iron in a formula isn’t a plus in itself: take it only for a confirmed deficiency.

Who should avoid hair vitamins

• Before any blood test – high-dose biotin, see above.
• In pregnancy – use a pregnancy supplement and don’t add beauty vitamins on top: they can contain preformed vitamin A.
• If you already take a multivitamin – add up zinc, selenium and vitamin A, which all have low upper limits.
• If you take medicines for epilepsy, your thyroid or blood thinning – check any formula with your GP or pharmacist.

How to choose hair vitamins on iHerb

1. Get tested and find out what you’re short of.
2. Correct that specific deficiency with a single supplement: iron, zinc or vitamin D.
3. If you buy a multi-ingredient formula, look for moderate doses: biotin in the hundreds of micrograms, zinc up to 15 mg.
4. Check it against your other supplements so you don’t double up on selenium and vitamin A.
5. Don’t expect quick results: hair grows slowly, so judge it over several months.

Our Supplement Facts guide explains how to read doses on a label. See the vitamin compatibility chart for combinations, and more guides in skin, hair and joints.