Acne causes several types of lesions, or pimples. Doctors refer to enlarged or plugged hair follicles as comedones. Types of acne include:

Whiteheads: Plugged hair follicles that stay beneath the skin and produce a white bump.Blackheads: Plugged follicles that reach the surface of the skin and open up. They look black on the skin surface because the air discolors the sebum, not because they are dirty.Papules: Inflamed lesions that usually appear as small, pink bumps on the skin and can be tender to the touch.Pustules or pimples: Papules topped by white or yellow pus-filled lesions that may be red at the base.Nodules: Large, painful solid lesions that are lodged deep within the skin.Severe nodular acne (sometimes called cystic acne): Deep, painful, pus-filled lesions.