Non-inflammatory Acne
Closed comedo, or whitehead.If the plugged follicle stays below
the surface of the skin, the lesion is called a closed comedo, or whitehead.
They usually appear on the skin as small, whitish bumps.
Open comedo, or blackhead. If the plug enlarges and pushes through the
surface of the skin, it's called an open comedo, or blackhead. The plug's dark
appearance is not due to dirt, but rather to a buildup of melanin, the skin's
dark pigment.
Inflammatory Acne
Papule. The mildest form of inflammatory acne is the papule, which
appears on the skin as a small, firm pink bump. These can be tender to the
touch, and are often considered an intermediary step between non-inflammatory
and clearly inflammatory lesions
Pustule. Like papules, pustules are small round lesions; unlike papules,
they are clearly inflamed and contain visible pus. They may appear red at the
base, with a yellowish or whitish center. Pustules do not commonly contain a
great deal of bacteria; the inflammation is generally caused by chemical
irritation from sebum components such as fatty free acids.
Nodule or Cyst. Large and usually very painful, nodules are inflamed,
pus-filled lesions lodged deep within the skin. Nodules develop when the
contents of a comedo have spilled into the surrounding skin and the local
immune system responds, producing pus. The most severe form of acne lesion,
nodules may persist for weeks or months, their contents hardening into a deep
cyst. Both nodules and cysts often leave deep scars.
Acne conglobata. This rare but serious form of inflammatory acne develops
primarily on the back, buttocks and chest. In addition to the presence of
pustules and nodules, there may be severe bacterial infection.
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