What Causes Acne?
Exactly why some people get acne and some do not is not fully known. It is known to be partly hereditary. Several factors are known to be linked to acne:
- Hormonal activity
- Hyperactive sebaceous glands
- Accumulation of dead skin cells
- Bacteria in the pores
- Skin irritation or scratching of any sort
- Anabolic steroids
- Birth control pills, however many women have reported reduced acne while on the pill
- Exposure to high levels of chlorine compounds, particularly chlorinated dioxins, can cause severe, long-lasting acne, known as Chloracne
How Does Acne Develop?
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.
Normal Pilosebaceous Unit
Diagram of a normal pilosebaceous unit, showing location of: Hair, Skin surface, sebum, follicle, and sebaceous gland.
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.
Types of Acne Lesions
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| Illustration of lesion, Microcomedo | Illustration of lesion, Open Comedo (Blackhead) | Illustration of lesion, Closed Comedo (Whitehead) |
Other troublesome acne lesions can develop, including the following:
- Papules--inflamed lesions that usually appear as small, pink bumps on the skin and can be tender to the touch
- Pustules (pimples)--papules topped by pus-filled lesions that may be red at the base
- Nodules--large, painful, solid lesions that are lodged deep within the skin
- Cysts--deep, painful, pus-filled lesions that can cause scarring.