Pimples have always been associated with adolescence, but this skin condition may be seen in adults too. There are various types of pimples, like whiteheads, blackheads, pustules, nodules, and cysts. Pimples can be found in both mild and severe forms. The basic cause for pimple formation is clogging of the tiny ducts that carry oil from the sebaceous glands to the pores on the skin. When exposed to air, the oil may get oxidized at the opening of the pore and turn black, thereby forming a blackhead. Pores that are clogged with oil may form whiteheads too. These blackheads and whiteheads are prone to infection, which in turn causes redness and swelling.