Acne vulgaris is the medical name for common acne – the presence of blackheads, whiteheads, and other types of pimples on the skin. The most common spots for breakouts are the face, chest, shoulders and back. Although mild acne may improve with over-the-counter treatments, more severe forms should be treated by a dermatologist.

Comedo is a hair follicle that has become clogged with oil and dead skin cells. Comedones can develop into bumps called whiteheads and blackheads.

Blackheads are comedones that are open at the surface of the skin. They are filled with excess oil and dead skin cells. It’s not dirt that causes the comedone to turn black. The black hue results from the irregular reflection of light coming from clogged hair follicles. Blackheads can frequently be treated with over-the-counter medications.

Whiteheads are comedones that stay closed at the surface of the skin. This happens when oil and skin cells prevent a clogged hair follicle from opening. Many of the same over-the-counter medicines that treat blackheads are also effective against whiteheads.

Papules are comedones that become inflamed, forming small red or pink bumps on the skin. This type of pimple may be sensitive to the touch. Picking or squeezing can make the inflammation worse and may lead to scarring. A large number of papules may indicate moderate to severe acne.

Pustules are another kind of inflamed pimple. They resemble a whitehead with a red ring around the bump. The bump is typically filled with white or yellow pus. Avoid picking or squeezing pustules. Picking can cause scars or dark spots to develop on the skin.

Nodules are large, inflamed bumps that feel firm to the touch. They develop deep within the skin and are often painful. Nodules should be treated by a dermatologist. Over-the-counter treatments may not be powerful enough to clear them up, but prescription drugs can be effective.

Acne mechanica is caused by heat, friction and pressure against the skin, often the result of wearing sports gear such as a helmet or baseball cap. It is sometimes called “sports-induced acne” because it occurs frequently in athletes. Preventive measures include wearing an absorbent material under sports equipment and showering immediately after activity.