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The four basic "causes" of acne
Acne is a disease of the
sebaceous
hair follicle (see diagram).
Each follicle contains a tiny hair and multilobed sebaceous glands.
((Diagram of the sebaceous gland))
Sebaceous glands get their name from the oily substance they produce -
sebum. Under normal circumstances, sebum travels up the
hair follicle and out to the skin's surface. However, in acne, sebum is trapped within the
follicle. Acne develops on those areas of the skin where sebaceous glands are most
numerous: the face, scalp, neck, chest, back, and upper arms and shoulders. The acne
lesions we know as blackheads are called "comedones" (singular:
comedo). Red, swollen, pus-filled
lesions are called papules,
nodules, and
pustules.
Four basic factors, work together for the development of comedones:
Each of these factors is discussed in more detail below.
Hormones
(androgens)
Acne usually begins when the body starts to produce the
hormones called androgens. When androgen production
goes into high gear - about age 11 to 14 years - acne also goes into high gear. Androgens
cause the sebaceous gland to enlarge, and this is normal. People who develop acne have
sebaceous glands that are over-stimulated by androgens. Young women tend to have acne
flare-ups that coincide with the hormonal changes associated with their menstrual cycle.
These changes affect the sensitivity of their sebaceous glands to androgens.
Increased sebum production
After the sebaceous gland is stimulated by androgens, it produces more
sebum. The oily sebum accumulate in the follicle, and travels up the hair shaft to the
surface of the skin. As it travels up the hair shaft it also mixes with normal skin
bacteria and dead skin cells that have been shed from the lining of the follicle.
The greater the sebum production, the greater the likelihood that the
hair follicle will become clogged and result in comedones.
Changes inside the follicle
As androgen production increases and sebaceous glands enlarge, the inner
lining of skin in the hair follicle also changes. Normally, dead cells inside the follicle
shed gradually and get expelled onto the surface. However, during puberty these cells are
shed more rapidly and tend to stick together. When they mix with sebum, they can clog the
follicle--the cells and sebum form a plug in the follicle.
Bacteria
The clogged follicle becomes a breeding ground for bacteria. One type of
bacteria specifically involved is
Propionibacterium acnes or
P. acnes
for short. P. acnes ingests sebum and is a normal resident on skin even in people
who don't have acne. However, when the sebaceous gland gets clogged, and sebum builds up
inside the follicle, P. acnes multiplies rapidly. Chemicals produced by
the bacteria can cause inflammation in the the follicle and surrounding skin.
Putting it all together...
Clogged follicles develop into two types of acne breakout:
(1) comedones, or non-inflamed 'blackheads', or
(2) inflamed lesions defined as papules, pustules, and nodules.
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to Why and how acne happens
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