About Acne
Doctors describe acne as a disease of the pilosebaceous units (PSUs).
Found over most of the body, PSUs consist of a sebaceous gland connected
to a canal, called a follicle, that contains a fine hair (see "Normal
Pilosebaceous Unit" diagram, below). These units are most numerous on
the face, upper back, and chest. The sebaceous glands make an oily substance
called sebum that normally empties onto the skin surface through the
opening of the follicle, commonly called a pore. Cells called keratinocytes
line the follicle
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The hair, sebum, and keratinocytes that fill the narrow follicle may
produce a plug, which is an early sign of acne. The plug prevents sebum
from reaching the surface of the skin through a pore. The mixture of
oil and cells allows bacteria Propionibacterium acnes (P. acnes) that
normally live on the skin to grow in the plugged follicles. These bacteria
produce chemicals and enzymes and attract white blood cells that cause
inflammation. (Inflammation is a characteristic reaction of tissues
to disease or injury and is marked by four signs: swelling, redness,
heat, and pain.) When the wall of the plugged follicle breaks down,
it spills everything into the nearby skin--sebum, shed skin cells, and
bacteria--leading to lesions or pimples.
People with acne frequently have a variety of lesions, some of which
are shown in the diagrams below. The basic acne lesion, called the comedo
(KOM-e-do), is simply an enlarged and plugged hair follicle. If the
plugged follicle, or comedo, stays beneath the skin, it is called a
closed comedo and produces a white bump called a whitehead. A comedo
that reaches the surface of the skin and opens up is called a blackhead
because it looks black on the skin's surface. This black discoloration
is not due to dirt. Both whiteheads and blackheads may stay in the skin
for a long time.
Acne lesions that can develop also include:
- Pustules (pimples)--papules topped by pus-filled lesions that may
be red at the base
- Papules--inflamed lesions that usually appear as small, pink bumps
on the skin and can be tender to the touch
- Cysts--deep, painful, pus-filled lesions that can cause scarring.
- Nodules--large, painful, solid lesions that are lodged deep within
the skin
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