角质素

例句：

1. 1. The skin is made up of keratin, which is a protein.
   皮肤由角质组成，这是一种蛋白质。
2. 2. Kérastase is a brand that specializes in keratin treatments.
   Kérastase是一家专门从事角质治疗的品牌。
3. 3. Keratin plays a crucial role in hair growth and repair.
   角质在头发生长和修复中起着关键作用。