Mild to Moderate acne vulgaris consists of the following types of acne spots:
Whiteheads: Whiteheads result when a pore is completely blocked, trapping sebum (oil), bacteria, and dead skin cells, causing a white appearance on the surface. Whiteheads are normally quicker in life cycle than blackheads.
Blackheads: Blackhead result when a pore is only partially blocked, allowing some of the trapped sebum (oil), bacteria, and dead skin cells to slowly drain to the surface. The black color is not caused by dirt. Rather, it is the skin's own pigment, melanin, reacting with the oxygen in the air. A blackhead tends to be a stable structure, and can often take a long time to clear.
Papules: Papules are inflamed, red, tender bumps with no head. Do not squeeze a papule. It will do no good, and may exacerbate scarring.
Pustules: A pustule is inflamed, and appears as a red circle with a white or yellow center. Pustules are your garden variety zit. 
