Acne is an umbrella term for a host of skin irritations and lesions including blackheads, cysts, pustules and whiteheads. Acne is caused by Propionibacterium acnes, and most types of acne are a result of the excess production of sebum, which is the oil produced by the sebaceous glands. When the sebaceous glands produce excess oil (this may be due to hormonal imbalances), the oil clogs up the pores and causes an inflammation or lesion.
The term acne includes various types of acne conditions, the most common of which is acne vulgaris. This condition is common among young males and females, and while it mostly affects the face, it can also develop on other parts of the body such as the torso and upper arms.
The smallest inflammation caused by acne is called a pustule. When oil breaks the surface, whiteheads are formed. When such oil comes in contact with air and is oxidized, it is called a blackhead. The next degree of inflammation is called a papule (or a pimple), and the deepest inflamed lesion is known as a cyst.
Cystic acne is a serious condition, in which cysts or nodules are formed on the skin. These nodules are large, painful and inflamed lesions which can cause significant trauma and scarring of the skin. Treatments for cystic acne can help to heal the cysts, but do not prevent scarring. The red patches caused by healing cysts are called macules. Macules do not cause lasting scars.