Many of these active agents are either peptides or proteins, yet skin is an extremely effective barrier that is highly impermeable to large molecular weight peptides and proteins.

• 许多活性剂不是多肽就是蛋白或兼之。但皮肤是一种非常有效的屏障，对这些大分子量的东西来讲是高度不可穿透的。