Pimples and whiteheads, called acne, occur when pores become clogged by the oil, bacteria and dead cells on the skin. Increased oil production can be caused by genetics, hormones or the environment.
Acne can occur when oil (sebum) and dead skin cells fill a pore. (See Ref 1, First section). If bacteria that naturally lives on our skin enters the pore it becomes inflamed. The inflammation will cause the pore to turn red and fill with pus. An inflamed pore is called a pimple. A pore that is filled with oil and dead cells, but is not inflamed, is a whitehead. (See Ref 3, Second Section). Acne can be caused by genetics and run in families. It can occur when hormones cause the skin to secrete increased oil, commonly seen in adolescents. And, may be the result of factors in the environment, like humidity or cosmetics.( See Ref 3, Third Section).