Sebum

Sebaceous glands secrete sebum. Also, these glands are found all over the body. The Latin word sebum means fat. Sebum acts like a barrier. Sebum coats the hair follicles then travels through the pores to eventually reach the skin. It prevents contaminants and viruses from penetrating the skin. Also, it keeps the skin very moist and hydrated so it does not dry out.

http://hair.lovetoknow.com/Hair_Follicles_Clogged_by_Sebum