2.1.1.2 Function of skin barrier
1.Defense physical damages
The skin has a certain mechanical strength，which can protect various mechanical forces such as friction and extrusion.The skin also has the ability to repair after being damaged.The melanin barrier in epidermis and protein barrier in stratum corneum can play a role of barrier by absorbing ultraviolet radiation.
2.Defense chemical damages
The skin has a certain barrier to various chemicals.The weak acidic environment on the surface of skin has the ability of buffering acids and bases.
3.Defense biological damages(https://www.daowen.com)
A complete skin barrier can be mechanically resistant to microorganisms.Antimicrobial peptides produced by the skin can kill bacteria，viruses，fungi and other microorganisms.In addition，the weak acidity of the skin and physiological desquamation of stratum corneum are not conducive to the growth and reproduction of microorganisms.
4.Prevent the loss of water，electrolyte and nutrients
The semi-permeable nature of the stratum corneum can prevent the loss of water，electrolyte and nutrients in the body.The sebaceous membrane on the skin's surface can also greatly reduce water loss.Under normal conditions，adults lose 240-480 mL of water through their skin every day（non-overt sweating）.However，if the stratum corneum is completely lost，the amount of water lost through the skin increases by more than 10 times each day.