Causes of 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. 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.
Combinations of several factors lead to the development of acne. It is thought that the layer of skin on or near hair follicles proliferate and shed abnormally which ends up plugging up the follicle altogether. Androgen hormones are thought to trigger this proliferation. Oils (sebum) that are normally produced by sebaceous glands (glands primarily associated with hair follicles) can accumulate in excess under the plug. Bacteria that normally reside on the skin, Propionibacterium acnes in particular, is thought to cause the associated redness, irritation and inflammation when directly involved.
Hair follicles. Aside from the palms of your hands and the soles of your feet, hair follicles exist virtually everywhere else on the body. Hair follicle complexes (pilosebaceous units) consist of a sebaceous gland that empties into a canal, called a follicle, that contains a hair (see "Normal Pilosebaceous Unit" diagram, above).
This canal is due to a natural invagination (folding of the outer layer) of the epidermis extending into the deep dermis. Associated arrector pili muscles (microscopic muscles attached to hair follicles which cause the hair to stand on end) and apocrine glands (a type of sweat gland) are also present in most cases.
The hair arises from the deep layers of the skin (dermis) while the sebaceous gland empties near the skin surface, just below the pore. Sebum produced from these glands are composed of oily secretions and degenerating epithelial cells that effectively coat the skin to lubricate, protect and prevent the skin against desiccation. Pilosebaceous units are especially abundant on the face, chest, back and scalp. Not surprisingly, these areas are hardest hit by acne.
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.
Androgens. Male hormones are often called androgens while female hormones are dubbed estrogens. These terms are often misunderstood since both men and women have androgens—men just have more of it. Androgen levels rise sharply at puberty, which causes the typical development of pubic hair, facial hair and voice changes in boys. These same androgens also affect the pilosebaceous unit by enlarging the sebaceous gland and increasing its sebum production. This sharp increase in production of oils throws off the normal oil to water ratio in the follicle and can lead to plug formation. Some examples of androgens known to play a role in acne formation are: testosterone, dihydrotestosterone (DHT) and dehydroepiandrosterone sulfate (DHEA-S).
Estrogens. These female hormones can act as a preventative measure against acne. It is no surprise that young women who have large amounts of estrogen are somewhat protected while older women who have diminished levels of estrogen are more susceptible to acne. Women who have especially large swings in the level of estrogen during their monthly menstrual cycles often show alternating periods of acne formation and acne healing. Birth control pills, which contain progesterone and estrogens, are often helpful in aiding the fight against acne for many young women.
Bacteria. Propionibacterium acnes is part of the normal flora of the skin. This bacteria is known to play a role in the redness and irritation associated with acne by releasing pro-inflammatory mediators (cytokines and tumor necrosis factor) through the hair follicle. P. acnes is also thought to manipulate the sebum produced by the sebaceous glands into a skin irritant. This bacteria thrives under this condition and multiplies almost uncontrollably.
Genetics. Acne vulgaris is thought to have a strong genetic factor.
Miscellaneous Factors. Anything that can manipulate or alter the above causes can contribute to acne formation. Some experts argue that severe stress can cause acne since stress levels play a role in the release of stress hormones that can affect the levels of androgens and estrogens in the body. Common skin irritations and rashes may affect the hair follicle itself (friction, tight clothing with tight collars). Cosmetics may play a role in helping plug hair follicles. Anabolic steroids, common medications (lithium, chlorides, iodides, barbiturates), and environmental exposure to halogen compounds have also been implicated in contributing to acne. Seemingly unrelated endocrine diseases that can skew the body’s response to hormone levels are also being studied (Cushing’s syndrome, congenital adrenal hyperplasia, polycystic ovary syndrome, etc).
Acne Myths. There are many myths about what causes acne:
- Diet. What you eat plays very little part in the development of acne. Eating lots of chocolate, greasy french fries, pizza and candy has not been implicated as causative agents of acne. There are currently studies being done on foods that may play a role in acne by manipulating hormone levels.
- Hygiene. Contrary to some beliefs, uncleanliness does not play a role in acne formation. The hair follicle plugs are a combination of excess sebum and shedding epithelial cells. P. acnes is a normal flora bacteria of the skin.
- Sex. Some people have reasoned that sexual activity, including masturbation, is linked to acne due to hormonal manipulation. This link has not been shown.
- Ordinary Stress. Daily stress has not shown to contribute to acne formation. Severe, life-altering stress levels however, can cause acne as a side effect.