Keratin is a structural protein naturally found in hair, skin, and nails. In the context of supporting the hair body system, keratin is most commonly used in topical hair treatments (such as shampoos and conditioners) and sometimes as a supplement. The rationale behind its use is that keratin can help to repair damaged hair, improve hair strength, and enhance overall hair appearance. Scientific evidence supporting the topical application of keratin is limited but does exist: some studies have shown that hydrolyzed keratin can penetrate the hair shaft and temporarily improve tensile strength and reduce hair breakage. For example, a study published in the International Journal of Cosmetic Science (2013) demonstrated that hydrolyzed keratin peptides could bind to hair fibers and improve mechanical properties.

However, the evidence is not robust or long-term, and most benefits appear to be cosmetic rather than systemic. There is little scientific support for oral keratin supplements improving hair health, since keratin is broken down in the digestive tract. The traditional use of keratin for hair health is limited, as keratin treatments are a relatively modern cosmetic development. In summary, while there is some scientific support for topical keratin improving the appearance and strength of hair, the evidence is modest and does not extend to systemic effects from supplements.