Does Biotin Make Your Hair Grow? Only if You're Deficient

Biotin makes your hair grow only if your body is truly short of it. If your levels are normal, extra biotin won't speed growth or thicken strands. Big doses can also scramble the blood tests that would find the real cause.

Maybe your hair started shedding and a bottle of biotin felt like a sensible first step. Maybe you've been taking it for a year and can't remember whether it ever did anything. Either way, the order matters: test first, supplement second.

Does Biotin Help Hair Growth?

Only when a deficiency or a specific condition is holding hair back. A 2017 review in Skin Appendage Disorders found 18 reported cases of biotin use for hair and nail changes. All of them improved, and every one had an underlying problem, such as an inherited or acquired biotin deficiency.

The authors concluded there is "lack of sufficient evidence for supplementation in healthy individuals." The NIH Office of Dietary Supplements is blunter. It says the hair and nail claims are supported, at best, by only a few case reports and small studies. The hair benefits come only from case reports in children.

So the before-and-after photos you've seen don't tell you much.

How Much Biotin Do You Need, and How Much Is in a Hair Supplement?

Adults need about 30 mcg a day, the same in pregnancy, and 35 mcg while breastfeeding. Food covers that easily for most people. The NIH lists one cooked egg at 10 mcg and 3 oz (85 g) of canned pink salmon at 5 mcg.

Hair supplements are a different scale. The American Thyroid Association says hair and nail products often provide 5,000 to 10,000 mcg, while multivitamins typically hold 30 to 300 mcg. That's roughly 170 to 330 times what an adult needs each day.

Your body doesn't turn that surplus into more hair. The NIH says there's no evidence biotin is toxic at high intakes, so no upper limit has been set. The real risk of a big dose sits somewhere else.

Does Biotin Affect Thyroid Tests and Other Blood Work?

Yes, and this is where hair supplements cause the most trouble. Some common lab tests use biotin as part of how they work, so high blood levels can make results read falsely high or falsely low.

The NIH describes case reports of biotin falsely suggesting Graves' disease and severe hyperthyroidism in people taking 10 to 300 mg a day. Even a single 10 mg dose interfered with thyroid tests done within 24 hours. That's 10,000 mcg, the top of the usual hair-supplement range.

Thyroid isn't the only one. The NIH also names tests for vitamin D and NT-proBNP, a heart-failure marker. The FDA says it has continued to receive adverse events reports of biotin causing falsely low troponin results.

Troponin is the test used to spot a heart attack. The NIH notes that, according to the FDA, one patient on high-dose biotin died after a falsely low result.

Why Biotin Can Hide the Cause of Your Hair Loss

Think about which tests a doctor orders when your hair is shedding. Thyroid problems are a known cause of hair loss, according to Mayo Clinic, so your doctor may well check your thyroid. The AAD says a dermatologist may order blood tests to look for a nutritional shortfall or hormone problem.

Thyroid and vitamin D results are among those biotin can distort. A thyroid result that looks overactive could send you down the wrong path, or one that looks normal could miss a real problem. How thyroid problems affect your hair covers what the results usually show.

Your doctor may not know to look for it. A Mayo Clinic study, summarized by the American Thyroid Association, checked 1,442 emergency department blood samples. In 107 of them (7.4%), biotin was above 10 ng/mL, a level that can interfere with common tests. Only 2 of those patients had biotin recorded in their medical records.

The ATA recommends stopping biotin for at least 2 days before thyroid testing. Tell whoever orders your blood work that you take it, and check whether your multivitamin or prenatal includes it. If a doctor prescribed biotin, or you take very high doses, ask them before stopping and how long to wait.

Is Biotin Deficiency Rare?

Severe deficiency is. The NIH says it "has never been reported" in healthy people eating a normal mixed diet. Lower levels show up in specific situations:

• Pregnancy. At least a third of pregnant women develop marginal deficiency despite normal intake, according to the NIH. Levels also fall while breastfeeding.
• Some seizure medicines. In a study of 264 people with epilepsy, a year or more on carbamazepine, primidone, phenytoin or phenobarbital was linked to lower biotin.
• Long-term heavy drinking, which reduces absorption.
• Eating raw egg whites often. A protein in raw egg white binds biotin, and cooking breaks it down.
• Biotinidase deficiency, a rare inherited condition that US newborns are screened for.

Low levels may be less rare in women with hair loss than that list suggests. One 2016 study of 466 women at a hair clinic found biotin deficiency in 38% of women complaining of hair loss. Deficiency there meant a blood level below 100 ng/L.

Even so, the author rejected treating women with hair loss indiscriminately. Biotin was advised only once a blood test showed a deficiency and linked it to the hair loss. Other causes, such as thyroid problems and low iron, were to be checked as well.

What Should You Do Instead of Taking Biotin?

Get tested before you supplement. The American Academy of Dermatology says you should only take biotin, iron, or zinc when your blood test shows a deficiency. It adds that many dermatologists suggest a multivitamin rather than single high-dose nutrients.

Ask about the likelier causes alongside biotin. Low iron and hair loss explains which iron numbers to ask for. Hormonal or nutritional hair loss helps you sort the pattern first.

Mayo Clinic lists pregnancy and childbirth among the hormonal causes of hair loss, and postpartum hair loss covers when it settles. Thinning at the edges after years of tight pigtails, braids or cornrows is a different problem. Mayo Clinic names that pulling as the cause of traction alopecia, and why your edges are thinning covers what helps.

When to See a Doctor

See a doctor or dermatologist if your hair loss is sudden or patchy, or you're losing more than usual when you comb or wash it. Mayo Clinic says early treatment of a receding hairline (frontal fibrosing alopecia, which mainly affects older women) might help avoid significant permanent hair loss.

Tell your doctor, too, if hair loss comes with signs of real biotin deficiency. The NIH lists a scaly red rash around the eyes, nose and mouth, pink eye, brittle nails, and tingling in the hands or feet.

If you have chest pain or think you're having a heart attack, call 911 (999 in the UK) or your local emergency number. Don't wait to stop biotin first. Just tell the staff you take it.

Frequently Asked Questions

How Long Does Biotin Take to Work for Hair?

If you're truly deficient, correcting it lets hair grow normally again. If your levels were normal, the evidence gives no reason to expect a change however long you take it.

Is 10,000 mcg of Biotin Too Much?

It isn't known to be toxic, but it's around 330 times the 30 mcg adults need. At that dose, even a single pill has interfered with thyroid tests within 24 hours, according to the NIH.

How Long Should You Stop Biotin Before a Blood Test?

The American Thyroid Association recommends at least 2 days before thyroid testing. For other tests, ask the doctor or lab that orders them, and always say you take biotin.