Acne remains a bit of a mystery. It seems to be partly hereditary, but why some people are affected by it and others are untouched isn't exactly known. We do, however, understand some of the biology behind it. The main culprit is the excess production of sebum, an oily substance whose function is to keep skin and hair lubricated and supple. The production of the oily sebum blocks the skin's surface, which provides an ideal environment for bacterial growth. The bacteria multiply, the skin area becomes red and inflamed, and then a pimple pops up. The Role Of Testosterone The excess production of sebum is caused by testosterone, the male hormone. However, testosterone is present in both males and females. During puberty, the body changes in its reaction to testosterone, thereby producing extra sebum. This irregular reaction, occurring mainly during adolescence, causes the skin -- particularly the face and upper torso -- to become oily. The sebum then combines with naturally occurring dead skin cells to block hair follicles. The body usually regulates its reaction to testosterone by the early 20s, and then the annoying acne clears up. Hair Follicle Theory Narrowing hair follicles could be involved with the production of acne -- so says a recent scientific theory. Evidence suggests that hair follicles may become restricted for several reasons, including excessive shedding of cells within the follicle, abnormal cell binding, or water retention which causes the skin to swell. The narrowed hair follicles prevent dead cells from being expelled from the body, creating a buildup beneath the skin. Combined with sebum, it produces ideal conditions for acne. Making Matters Worse Many people can't resist squeezing their pimples. This may make the condition worse, by spreading the bacteria to the surrounding skin area. It also can lead to scarring, sometimes permanently. Even touching the face can worsen acne. Without realizing it, most of us touch our faces many times throughout the day. The problem is that our hands contain oils and bacteria that will increase the acne symptoms. In fact, all objects, including eyeglasses and telephone handsets, that make contact with the face must be clean. Hair, particularly long hair, also touches your face, so it is important to keep your hair clean and oil free. Fabric accessories such as hats and headbands should be avoided or used as little as possible. Other Factors Other things that seem to aggravate acne conditions include diet, skin irritation, stress, hormonal activities such as menstrual cycles, and certain medications. Dietary links show skim milk products to be related to acne. There is no statistical evidence, however, that foods such as chocolate and fast food have any association with pimples or aggravates acne. Medications associated with acne include anabolic steroids (used for bodybuilding), lithium, barbiturates, halogens, and androgens.