The Label
Biotin — 5000 mcg
The nutrient most people already associate with hair and nails. Here is what it is, what it does, and what our figure means.
What Biotin Is
Biotin is a water-soluble B vitamin, sometimes written as vitamin B7 and occasionally as vitamin H, from the German Haar und Haut — hair and skin. It was identified in the 1930s by researchers investigating why animals fed enormous quantities of raw egg white developed dermatitis and lost their coats. Raw egg white contains avidin, a protein that grips biotin so tightly it cannot be absorbed at all.
That is where its reputation was born, and the reputation has outrun the evidence ever since. Biotin does something specific and important. It does not do everything the category implies.
What It Does
In hair
Five carboxylase enzymes in your body cannot function without biotin attached to them, and those enzymes handle branched-chain amino acid metabolism — the same amino acids that make up a great deal of keratin. Keratin is what a hair shaft is. A shaft built with everything available is a shaft that resists being washed, dried, brushed and tied up, which is why biotin reports are almost always about breakage rather than growth rate.
In nails
The clearest human evidence for biotin sits here. Small studies in the late 1980s and 1990s found measurable increases in nail plate thickness in people with brittle nails taking supplemental biotin over several months. The studies were small and uncontrolled by modern standards, and they remain the most encouraging data anyone has on this nutrient.
In skin
Frank biotin deficiency produces a distinctive scaly rash around the eyes, nose and mouth, which resolves when biotin is restored. That is the mechanism by which biotin matters to skin, and it is worth stating precisely: it is a deficiency correction, not an enhancement in people who were never short.
Our Amount
5000 mcg In Every Serving
Our serving carries 5000 mcg. An adult adequate intake is around 30 mcg a day, so this is well over a hundred times that figure. It is the number this entire category settled on rather than one derived from a trial in healthy people, and we use it while telling you exactly what it does to a blood test.
Biotin is the cofactor five different carboxylase enzymes cannot work without, and those enzymes sit right where your body handles the amino acids keratin is assembled from. Keratin is the protein your hair shaft and your nail plate are built out of, which is how a B vitamin ends up mattering to the tips of your fingers.
When People Fall Short
True biotin deficiency is genuinely rare, because gut bacteria make some and the requirement is small. It shows up mainly in people on long-term anticonvulsants, people with a rare inherited enzyme disorder, people who eat large amounts of raw egg white, and occasionally in pregnancy, where marginal biotin status is more common than most people expect.
The signs, when it happens, are a scaly red rash around the face, thinning hair, brittle nails, and neurological symptoms in more severe cases.
Where It Occurs In Food
| Source | Roughly | Notes |
|---|---|---|
| Cooked egg yolk | Roughly 10 mcg per egg | Cooking denatures the avidin in the white, which is why cooked eggs are a source and raw ones are the opposite |
| Liver | 30–40 mcg per 75 g | By a distance the richest ordinary food source |
| Salmon | About 5 mcg per 75 g | Modest but reliable |
| Sunflower seeds | About 2.6 mcg per 30 g | Easy to add to an ordinary day |
| Almonds | About 1.5 mcg per 30 g | Small amounts, frequently |
| Sweet potato | About 2.4 mcg per half cup | Also carries the carotenoids |
The Ceiling, And The Cautions
No upper intake limit has been established for biotin. Excess is water soluble and excreted, and toxicity is not the concern.
Laboratory interference is the concern, and it is a serious one. Biotin at supplemental levels interferes with a wide range of immunoassays. Thyroid function panels are the most commonly affected, and cardiac troponin — the test used to diagnose a heart attack — is the most consequential. Interference can push a result in either direction. Tell whoever draws your blood that you take a 5000 mcg biotin supplement, and ask whether to pause it for a few days beforehand.
Answers
Biotin Questions
The questions we are asked about this nutrient specifically.
Does biotin make hair grow faster?
Almost certainly not. Growth rate is set largely by your follicles. What biotin plausibly influences is how well the shaft is assembled and therefore how much of it survives daily handling.
Is 5000 mcg too much?
There is no toxicity ceiling and the excess is excreted. The practical consequence is laboratory interference rather than harm, which is manageable as long as it is declared before a blood draw.
Can biotin cause acne?
It is reported anecdotally and the proposed mechanism involves competition with pantothenic acid for absorption. The evidence is thin. If your skin worsens consistently after starting, stop and see whether it settles.
How long before nails change?
Nail grows about three millimetres a month, so any change appears near the cuticle first and takes six to eight weeks to become visible at all.