Whiteheads & Blackheads
A mass of solidified sebum, dead skin cells and other material White or cream-colored
Comedones that stay below the skin surface produces a white bump that is clogging the follicle, but that has not expanded enough to force open the follicle called a whitehead, this bump ranging in size of a pinhead to as large as the tip of the little finger, where as open comedones that reaches the skin surface produces a black plug called a blackhead. The black color of the blackhead is not caused by dirt or oxidation.
Neither whiteheads nor blackheads should be squeezed or "popped" without proper medical supervision under sterile conditions. This is because injured lesions can become infected and/or scarred.

Who Gets Acne
Acne is found in people of all races and ages. Almost all adolescents and young adults develop acne - indeed, nearly 85% of people between the ages of 12 and 24 have acne. For most, acne goes away by the time they reach their thirties. However, for some, acne can develop well into adulthood.
Acne affects young men and women about equally. However, young men are more likely to suffer from more severe and longer lasting forms of acne. Young women are more likely to suffer from intermittent acne caused by hormonal changes associated with their menstrual cycles or from acne caused by cosmetics.

Other Types of Acne Lesions
A papule is a small (less than 5 mm), inflamed solid lesion that appears as small, pink bumps on the skin. A group of small papules may not be visible to the eye, but can have a "sandpaper" feel and be tender to the touch.

Pustule (Pimple)
A pustule is a dome-shaped lesion filled with pus containing a mixture of white blood cells, dead skin cells, and bacteria. Often red at the base, a pustule that forms over a hair follicle usually has hair in the center. Normally, pustules that are resolved without turning into cysts do not leave any scars

Nodule
Similar to a papule, a nodule is a dome-shaped or irregularly shaped lesion. However, a nodule is deeper than a papule, and can cause pain and/or scarring.

Cyst
A cyst is a deep and painful lesion filled with pus containing a mixture of white blood cells, dead skin cells, and bacteria. It is usually larger than a pustule and can lead to scarring. This condition is usually referred to as cystic acne.

Red Spot (Macula)
Red spots or maculae are usually flat, pinkish red in color at first, with a well-defined border. Untreated, maculae normally go away on their own after 4 to 6 months, and may change into a darker brownish red color before clearing up. Maculae typically disappear without any trace or scars

Post-Inflammatory Pigmentation
This form of pigmentation occurs at the site of the healed or healing acne, especially in people with darker skin tones. Some post-inflammatory pigmentation can last up to almost 2 years, especially with excessive sun exposure.

Acne Scars
Scars caused by injury to the skin tissue and the subsequent repair process. In cases of acne, especially deep acne, tissue injury is the result of the body's inflammatory response to the dead cells and bacteria in the plugged sebum.
In most cases, only nodule and cystic acne are associated with scarring. In people who are prone to scarring, however, common acne lesions may result in permanent scars.

There are two types of scars:
Those caused by increased tissue formation and those caused by loss of tissue.
In the first type, called keloids, skin injury from acne inflammation causes the cells to overproduce collagen, resulting in increased tissue formation. Typical keloid scars are a series of solid, irregular bumps about 1 to 2 mm in diameter. This form of scar is rare, and usually only affects people with a family history of keloid scarring.
A more common scarring associated with acne is that caused by tissue loss, such as the ice-pick scar. Usually occurring in the cheeks, ice pick scar forms when deep and shallow indentations or holes are left by acne.