It’s a condition that is caused by the overproduction of sebum. Sebum is an oily substance that forms in glands just under the surface of the skin called sebaceous glands. Sebum normally flows out hair follicles onto the skin to act as a natural skin moisturizer. The glands are connected to hair follicles that allow the sebum, or oil, to empty onto the skin through a pore. If hair follicles become blocked by sebum, dead skin cells, and bacteria, acne is the result.
It usually begins at puberty and worsens during adolescence. Nearly 85 percent of people develop pimples at some point between ages 12 to 25. As many as 20 million teens have the condition. It may appear as early as age 10, and even may be found in some newborns. Some people may continue to be affected by acne after age 30.
During puberty, there are increased levels of the male hormone androgen. High levels of androgen cause excess sebum to form. Sometimes the sebum combines with dead, sticky skin cells and bacteria called Propioni-bacterium acnes (P. acnes) that normally live on the skin. The mixture of oil and cells allows the bacteria to grow in the plugged follicles. When this happens, a hard plug called a comedo can form. A comedo is an enlarged hair follicle.