Biotin, also known as vitamin B7, is commonly marketed as a supplement to support hair health. Its use is based on its essential role in cellular metabolism, particularly in the metabolism of fatty acids, amino acids, and glucose, all of which are important for the maintenance of healthy hair, skin, and nails. Scientifically, biotin deficiency is known to cause hair thinning and loss, as well as brittle nails and skin rashes. Supplementation in individuals with a demonstrated deficiency has been shown to improve these symptoms, including hair regrowth.

However, most people obtain adequate biotin through their diet, and biotin deficiency is quite rare in developed countries. For individuals without a deficiency, current scientific evidence does not strongly support the use of biotin supplements for improving hair growth or quality. Clinical trials in individuals with normal biotin levels have generally failed to show significant benefits from supplementation. The widespread belief in biotin’s benefits for hair among the general population is therefore not strongly backed by large, high-quality studies; rather, it is extrapolated from its role in deficiency states.

In summary, while biotin supplementation is scientifically justified and effective for those with biotin deficiency, evidence supporting its use for hair health in otherwise healthy individuals is limited and weak, justifying a modest evidence rating.