TABLE 2.

Definitions of lesions

LESION	DEFINITION
Comedo	Sebaceous follicle plugged with sebum, dead cells from inside the sebaceous follicle, tiny hairs, and sometimes bacteria. When a comedo is open, it is commonly called a blackhead because the surface of the plug in the follicle has a blackish appearance. A closed comedo is commonly called a whitehead; its appearance is that of a skin-colored or slightly inflamed “bump” in the skin.
Papule	Small (5mm or less), solid lesion slightly elevated above the surface of the skin. A group of very small papules and micro-comedones may be almost invisible but have a “sandpaper” feel to the touch. A papule is caused by localized cellular reaction to the process of acne.
Nodule	Dome-shaped or irregularly shaped lesion. Unlike a papule, a nodule is characterized by inflammation, extends into deeper layers of the skin, and may cause tissue destruction that results in scarring.
Cyst	Sac-like lesion containing liquid or semi-liquid material consisting of white blood cells, dead cells, and bacteria. It is larger than a pustule, may be severely inflamed, extends into deeper layers of the skin, may be very painful, and can result in scarring.