Comedones that stay closed at the surface of the skin are called whiteheads. 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, painful, solid lumps that are lodged deep in the skin.