Efficacy and Safety of L-Cystine Associated or not to a Natural Keratin (Kera-Dietandreg;) Hydrolysate on Hair and Nails: Randomised, Placebo-Controlled, Clinical Trial on Healthy Females

In a 2019 randomized, placebo-controlled clinical trial involving 60 healthy female subjects with acute telogen effluvium and brittle nail syndrome, researchers found that L-Cystine (CYS) alone or in combination with a natural keratin hydrolysate (Kera-Diet® or KDC) significantly improved hair density, hair and nail brightness, and nail growth rate over a 3-month period. The study reported a 56.9% and 58.9% increase in hair brightness for the CYS and KDC groups, respectively, and a nail growth rate of 0.21 ± 0.02 mm/14 days for the KDC group after 90 days. The treatments were well tolerated with no adverse reactions, and a self-assessment questionnaire indicated a 90% global satisfaction rate for the combination treatment. The study concluded that both L-Cystine and the combination with Kera-Diet® are effective and safe for improving hair and nail parameters in healthy females, offering a beneficial dietary approach for managing symptoms of acute telogen effluvium and brittle nail syndrome.