If the plug breaks open, the material inside causes swelling and red bumps to form.
If the inflammation is deep in your skin, the pimples may enlarge to form firm, painful cysts.
Acne is a problem of swelling and inflammation, not a problem caused by bacteria.
Acne is most common in teenagers, but it can happen at any age, even in an infant. Three out of four teenagers have some acne. Hormonal changes probably cause increased oil in the skin. However, people in their 30s and 40s may also have acne.
Acne tends to run in families and can be triggered by:
Hormonal changes related to menstrual periods, pregnancy, birth control pills, or stress