Silica, often in the form of silicon dioxide or as the bioavailable compound orthosilicic acid, is marketed as a supplement to support hair health, including reducing hair loss and thinning. The rationale is based on the role of silicon in the synthesis and stabilization of connective tissue components such as collagen, which are important structural elements in hair, skin, and nails. There is some scientific basis for its use, with a handful of small-scale clinical studies and laboratory research suggesting that silica supplementation may improve hair tensile strength, thickness, or quality. For example, a 2007 randomized, double-blind, placebo-controlled study found that women who took choline-stabilized orthosilicic acid for nine months experienced increased hair tensile strength compared to placebo. However, the number and size of such studies are limited, and the overall quality of evidence is modest. No large, well-powered clinical trials have firmly established silica's efficacy for treating hair loss or thinning, and the mechanism by which it might influence hair growth in humans is not fully understood. Thus, while there is some scientific validation, it remains preliminary, and silica should not be regarded as a primary or stand-alone treatment for hair loss. Most authoritative dermatology guidelines do not list silica as an evidence-based therapy for alopecia.