What causes acne?

No one factor causes acne. Acne happens when oil (sebaceous) glands come to life around puberty, stimulated by male hormones from the adrenal glands of both boys and girls. Sebum (oil) is a natural substance which lubricates and protects the skin, and under certain circumstances, cells that are close to the surface block the openings of sebaceous glands and cause a buildup of oil underneath. This oil stimulates bacteria (which live on everyone's skin and generally cause no problems) to multiply and cause surrounding tissues to become inflamed.
Inflammation near the skin's surface produces a pustule; deeper inflammation results in a papule (pimple); deeper still and it's a cyst. If the oil breaks though to the surface, the result is a "whitehead." If the oil accumulates melanin pigment or becomes oxidized, the oil changes from white to black, and the result is a "blackhead." Blackheads are therefore not dirt, and do not reflect poor hygiene.

Here are some factors that don't usually cause acne, at least by themselves:

Heredity: With the exception of very severe acne, most people do not have the problem exactly as their parents did. Almost everyone has some acne at some point in their life.
Food: Parents often tell teens to avoid pizza, chocolate, greasy and fried foods, and junk food. While these foods may not be good for overall health, they don't cause acne or make it worse. Although some recent studies have implicated milk and dairy products in aggravating acne, these findings are far from established.
Dirt: As mentioned above, "blackheads" are oxidized oil, not dirt. Sweat does not cause acne, therefore, it is not necessary to shower instantly after exercise for fear that sweat will clog pores. On the other hand, excessive washing can dry and irritate the skin.

Stress: Some people get so upset by their pimples that they pick at them and make them last longer. Stress, however, does not play much of a direct role in causing acne.

Hormones: Some women break out cyclically, but most women (and men) don't. Some oral contraceptive pills may help relieve acne, but unless a woman has abnormal menstrual periods and excessive hair growth, it's unlikely that hormones play much of a role in causing acne.

Pregnancy has a variable effect on acne; some women report that they clear up completely, and others get worse, while many others see no overall change.

Cosmetics: Most cosmetic and skin-care products are not pore-clogging ("comedogenic"). Of the many available brands, those which are listed as "water-based" or "oil-free" are generally a better choice.

In occasional patients, the following may be contributing factors:
Pressure: In some patients, pressure from helmets, chinstraps, collars, suspenders, and the like can aggravate acne.

Drugs: Some medications may cause or worsen acne, such as those containing iodides, bromides, or oral or injected steroids (either the medically prescribed prednisone or the steroids that bodybuilders or athletes take). Other drugs that can cause or aggravate acne are anticonvulsant medications and lithium, which is used to treat bipolar disorder. Most cases of acne, however, are not drug-related.

Occupations: In some jobs, exposure to industrial products like cutting oils may produce acne.


** stress and hormones