Acne is one of the most common skin diseases in the United States, report doctors at the American Academy of Dermatology. While acne is more common among teens and young adults, the skin condition can affect anyone. There are a number of contributing factors that determine the level of severity of acne, which is especially problematic for people with fluctuating hormones. There are various types of acne skin diseases, ranging from cysts and nodules to inflammation that creates pimples, blackheads and whiteheads.

Postules

Postules are very common and, typically, do not leave acne scars. A postule is a tender bump that is filled with pus. The pus in postules, often referred to as pimples, is made up of dead skin cells, bacteria and white blood cells. Most postules form over a hair follicle that has been stopped up with dirt or oil. Postules usually heal on their own with over-the-counter acne treatments.

Comedo

Comedones are clusters of comedo that usually are referred to as blackheads and whiteheads. Usually, a comedo is formed when a hair follicle becomes clogged with dirt and oil. An open comedo is called a blackhead, because the hair pokes out from under the skin and appears as a black spot on the skin. A closed comedo is a whitehead and grows underneath the surface of the skin and, usually, is filled with some pus. Squeezing comedones is not recommended, because infection can set in and create worse problems. Over-the-counter, topical, drying agents and mild cleansers are best to use to treat comedones, so that there is no resultant scarring.

Nodule

A nodule is like a postule, only bigger and deeper. It, too, has a dome-shaped appearance and is filled with pus. A nodule is surrounded by inflammation that extends deep into the layers of the skin and may show on the top layer of skin as redness around the pimple. A nodule can be painful and leave a scar because of the deep tissue damage. Nodules are a severe acne skin disease that often do not respond to over-the-counter, topical, acne creams and must be treated with isotretinoin.

Cysts

Cysts are large, sac-like pimples that often occur in conjunction with nodules. They, too, are filled with bacteria and dead skin cells and travel to the deeper layers of the skin. Cysts are painful lesions that often leave permanent scars. Severely inflamed nodules often are mistaken for cysts, report doctors at the American Academy of Dermatology. Treatment of cysts must be systemic. The most common treatment is isotretinoin.