polypeptide of L lysine - Polylysine can inhibit the growth of microorganisms, and specifically produce an antimicrobial effect against yeast, fungi, and bacteria, according to Wikipedia.

Polylysine may have anti-aging properties as well, due to its protein and amino acid content. According to an article on Amino Acids for Anti-Aging, "Amino acids ... act by attaching to skin cells to fill in lines and make skin appear smoother, in addition to improving skin tone and color, providing exfoliation, reducing fine lines and wrinkles, and minimizing the appearance of photodamage." Amino acids are powerful anti-aging ingredients because of their ability to communicate with cells, improving their ability to affect aging cells and repair them.

In a patent filed by L'Oreal, Polylysine is also noted as having the ability to "improve the surface state of keratin fibres," a strong protein involved in hair and nail growth.