Also known as acne vulgaris or acne, pimples are a common skin infection which usually occurs when one hits puberty. It is characterised by a red swelling, the size of a boil on the face, neck or back. It is a result of the increase in the production of the hormone testosterone in both males and females. Excess secretion of sebum (oily liquid which prevents the skin from drying) also leads to the formation of acne. Other factors like dirt, oil, clogged pores, and wrong diet are also responsible for pimples. Certain medications that contain corticosteroids, androgens or lithium can also produce acne.