L-lysine is an essential amino acid that has been studied for its potential role in supporting hair health. Scientifically, L-lysine is necessary for overall protein synthesis, which includes the production of keratin, the primary protein in hair. Some evidence suggests that L-lysine may help with hair growth, especially in cases where hair loss is linked to a deficiency in this amino acid. For example, a study published in Clinical and Experimental Dermatology (2002) found that women with chronic telogen effluvium (a form of diffuse hair loss) who supplemented with L-lysine and iron experienced better hair regrowth than those who used iron alone. The proposed mechanism is that L-lysine enhances iron absorption and utilization, which is important because iron deficiency can contribute to hair loss, particularly in women.

However, while these findings are promising, the overall scientific evidence is limited and not robust. Most studies are small, and there is a lack of large, well-controlled clinical trials. There is no direct evidence that L-lysine supplementation benefits hair growth or prevents hair loss in otherwise healthy individuals without a lysine deficiency. Therefore, while there is some scientific rationale and preliminary evidence supporting the use of L-lysine for hair health, the strength of the evidence is moderate at best.