Acne

A small inflamed elevation of the skin : papule; especially : pustule. 2 : a swelling or protuberance like a pimple.
Also known as spots or zits, pimples are a part of acne. They are most likely to occur around puberty, but they can happen at any age.
During puberty, hormone production changes. This can cause the sebaceous glands, located at the base of hair follicles, to become overactive. As a result, pimples are most likely to occur during the teenage years and around menstruation, for women.
Pimples most often affect the face, back, chest, and shoulders. This is because there are many sebaceous glands in these areas of skin.
Acne vulgaris, the main cause of pimples, affects over 80 percent of teenagers. After the age of 25 years, it affects 3 percent of men and 12 percent of women.
Fast facts on pimples
pimples range in severity, from blackheads to cysts.
they happen when the sebaceous glands become more active, dead skin cells clog the pores, and sometimes an infection develops.
pimples often occur in adolescence, but they can affect people at any age.
there is not enough evidence to confirm that any particular food causes acne, but following a healthful diet may reduce the risk.

Types
There are several different types of pimples, and they have different signs and symptoms:
Whiteheads: also known as a closed comedo, these are small pimples that remain under the skin. They appear as a small, flesh-colored papule.
Blackheads: also known as an open comedo, these are clearly visible on the surface of the skin. They are black or dark brown, due to the oxidation of melanin, the skin's pigment.
Some people mistakenly believe they are caused by dirt, because of their color, and scrub their faces vigorously. Scrubbing does not help. It may irritate the skin and cause other problems.
Papules: these are small, solid, rounded bumps that rise from the skin. They are often pink.
Pustules: these are pimples full of pus. They are clearly visible on the surface of the skin. The base is red and the pus is on the top.
Nodules: these have a similar structure to papules, but they are larger. They can be painful and are embedded deep in the skin.
Cysts: these are clearly visible on the surface of the skin. They are filled with pus and are usually painful. Cysts commonly cause scars.