|
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.
|
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, leading to lesions
or spots. |
 |
|
Normal Pilosebaceous
Unit
|
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, 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, but
looks black due to the air oxidising inside.
Both whiteheads and blackheads may stay in the skin for a long time.
Types of Lesions
Other troublesome acne lesions can develop, including the following:
Papules
These are inflamed lesions that usually appear as small, pink
bumps on the skin and can be tender to the touch.
Pustules (spots / zits)
These are papules topped by pus-filled lesions that may be red at
the base.
Nodules
These are large, painful, solid lesions that are lodged deep
within the skin.
Cysts
These are deep, painful, pus-filled lesions that can cause scarring.
For information about acne treatments,
click here
|
