Skin is not absolutely tight and permeable, it can selectively absorb nutrients from outside. There are three ways for skin to absorb nutrients directly from outside:
⑴.It softens the stratum corneum, penetrates through the cell membrane of the stratum corneum, enters the cells of the stratum corneum, and then passes through the other layers of the epidermis;
⑵. A small amount of macromolecules and water-soluble substances can be absorbed through pores and pore;
⑶. A small amount of nutrients penetrate into the dermis through the surface cell space.