What's in a hair supplement

You're standing in the pharmacy aisle with a box in each hand. One says "hair and nails". The other says "hair strength and vitality". You turn them over and read the ingredients: biotin, zinc, selenium, cystine, millet extract. They're almost identical. So what's actually in these capsules, and what do we know about whether they work?

What's in the capsule

From one brand to the next, the same families of ingredients keep coming back.

• B vitamins: biotin (vitamin B7, sometimes called B8), vitamin B5 (often listed as calcium pantothenate), B6, and sometimes niacin (B3).
• Minerals: zinc, selenium, copper, sometimes iron.
• Amino acids, the building blocks of protein. The most common is cystine (or cysteine), which is rich in sulphur, like the keratin hair is made of.
• Plant or marine extracts. Millet seed extract contains silica, amino acids, vitamins and minerals¹.

The products reviewed by the European guideline on hereditary hair loss are typical of these blends: cysteine, histidine, copper and zinc in one; cysteine, calcium pantothenate and millet in another; marine extracts and silica in a third¹.

Here's a surprise: the same ingredient can be sold under two different statuses. In France, a combination of cystine and vitamin B6 is also sold as an over-the-counter medicine, presented as a supporting treatment for brittle nails and hair².

What the label is allowed to say

In Europe, a supplement can't promise just anything. The health claims it may make are listed in an EU regulation. For hair, there are only four³:

• biotin contributes to the maintenance of normal hair;
• zinc contributes to the maintenance of normal hair;
• selenium contributes to the maintenance of normal hair;
• copper contributes to normal hair pigmentation.

Read those words again: maintenance of normal hair. They mean these nutrients are part of what your body needs to make hair. None of them says they slow shedding, thicken hair or make it grow back. When a package hints at more, that's marketing, not an authorised claim.

What the studies show

The European S3 guideline, written by dermatologists on hereditary hair loss (androgenetic alopecia), reviewed these products. Its finding: most contain several substances at once, so you can't tell which ingredient does what, and there's only one study, two at most, per product¹.

Some results are positive. In 40 women, a blend of cysteine, calcium pantothenate and millet taken for 6 months increased the share of hairs in the growth phase compared with a placebo¹. For zinc and copper, only ever tested in blends, the evidence is judged insufficient. The same goes for iron when there's no deficiency¹. In the end, the authors recommend these products neither for nor against: the decision is left to the dermatologist and the patient¹.

A systematic review published in JAMA Dermatology in 2023 went further. Out of more than 6,300 records, it kept 30 publications, including 17 randomised trials⁴. The authors cautiously conclude that supplements may have a role, but call for larger trials compared against established treatments, and point out that each result has to be read in light of how the study was run⁴. Several of these trials tested specific commercial products: a result from one formula doesn't carry over to another.

When it helps: a deficiency

Where everyone agrees is on deficiency. The American Academy of Dermatology puts it simply: if you don't get enough biotin, iron, protein or zinc, you can lose noticeable amounts of hair, and it can grow back once the shortfall is fixed⁵. A review on diet and hair loss says the same: a deficiency should be corrected⁶.

Biotin is a good example. A real deficiency does cause hair loss, but it's rare, because gut bacteria usually make enough. And no clinical trial has shown that it treats hair loss in someone who isn't deficient⁶.

There's only one way to find out if you're short of something: talk to your doctor, who can order a blood test. Taking a capsule "just in case" won't tell you.

What people who took them say

On an English-language hair loss forum, members shared how biotin worked for them⁷⁸. Opinions are mixed, and often unsure.

Posts on the HairLossTalk forum⁷⁸.

That "who knows?" says it all: with nothing to compare against, you can't tell whether a product changed anything.

More isn't better

A supplement isn't harmless just because you can buy it without a prescription. Some excesses do the opposite of what you want.

• Taking large amounts of vitamin A or selenium is toxic and can cause hair loss⁵.
• Selenium shows up in some hair supplements, even though it has barely been studied in human hair loss⁶.
• Iron taken without monitoring can build up in the body until it becomes toxic⁶.
• Too much zinc can cause stomach pain, vomiting and diarrhoea; over time, it interferes with iron and weakens the immune system⁶.

Watch out for doubling up, too. A hair capsule, a multivitamin and a "skin" supplement can contain the same vitamins, and the amounts add up. If you already take medication, or if you're pregnant or breastfeeding, ask your doctor or pharmacist before adding anything.

Before a blood test

Biotin has a little-known side effect: it can skew some blood test results. France's medicines agency, the ANSM, explains that many lab tests use biotin in how they work, and the biotin you swallow can throw off the result. This affects, for example, tests for hormones, tumour markers, proteins and viral infections⁹.

If you take a supplement that contains it, tell the lab before a blood test. And if you use a home test, check that its leaflet doesn't mention interference with biotin⁹.

Judge by photos, not by feel

A course of supplements often lasts several months, and hair grows slowly. After three months, the question comes back: is it doing anything? In the mirror, the answer depends mostly on the daylight and your mood.

To judge fairly, you need a starting point. Take photos before you start, then the same photo every week: same room, same light, same distance, hair dry and styled the same way. Aim at your parting, the crown and the temples.

That's what Calvap does. Last week's photo shows as an overlay so you can line yourself up exactly the same way, and the log keeps the date you started or stopped a product. Calvap shows you, with photos, whether anything has changed. And if you see a doctor, you bring dated pictures instead of "I think it's better".