Biotin, also known as vitamin B7, is commonly promoted as a supplement to support nail health, especially to strengthen brittle nails. Scientific evidence for biotin’s effectiveness in improving nail strength is limited but does exist. Several small studies, including early research from the 1980s and 1990s, have found that biotin supplementation (typically 2.5 mg per day) can increase nail thickness and reduce nail brittleness in some individuals with brittle nail syndrome. For example, one uncontrolled study reported that 63% of participants experienced improvement in nail firmness and hardness after several months of biotin supplementation. Another small study observed increased nail plate thickness in some subjects.

However, these studies are limited by small sample sizes, lack of control groups, and potential bias. There is no strong evidence that biotin supplementation benefits people with normal, healthy nails. Most research supporting biotin for nails is focused on individuals with documented biotin deficiency or brittle nail syndrome, which is relatively rare. Major health authorities, such as the National Institutes of Health (NIH), note that while biotin may help certain people with weak or brittle nails, robust clinical trials are lacking.

In summary, while there is some scientific evidence suggesting biotin may support nail strength in individuals with brittle nails, the overall quality and quantity of evidence is low. Biotin is not universally effective for improving nail health in the general population.