Acne overview

Acne lesions have several types:

• Comedone / Microcomedone: Comedone is enlarged hair follicle plugged with oil and bacteria. This is the first and smallest type of lesion. It is often called microcomendone because it cannot be seen by the naked eye.
• Open comedone / blackhead: Open comedone a.k.a. blackhead is a plugged follicle that reaches the surface of the skin. Although dark in appearance, blackheads do not indicate the presence of dirt. The dark color comes from chemically altered oils and bacteria.
• Closed comedone / whitehead: Closed comedone a.k.a. whitehead is a clogged follicle that stays beneath the skin. Whiteheads usually appear on the skin as round, white bumps 1-2 mm wide.
• Papules: Papules are inflamed lesions that appear as small, pink bumps on the skin. They do not contain any visible puss.
• Pustules / pimples: Pustules or pimples are inflamed pus-filled lesions red at the base
• Cysts and nodules: These are large, inflamed, pus-filled lesions that are lodged deep and can drain, causing pain and scarring.
• Scars: As they heal, acne lesions, particularly cysts and nodules and, less frequently, pistules may cause scars of various shape and size.

How acne lesions develop

Excessive secretion of oils from the sebaceous glands combines with naturally occurring dead skin cells to block the hair follicles. Sometimes, excessive or altered keratinization (hardening and death of epithelial cells) leads to abnormal shedding of the skin lining of the pores. Oil secretions build up beneath the blocked pore, forming a comedone, which is a perfect anaerobic environment for the growth of the skin bacterium Propionibacterium acnes. Bacterial growth triggers inflammatory response, producing an inflamed lesion, such as a pustule or a nodule. After an inflamed lesion heals, a scar may develop.

Causes of acne

Development of acne requires a combination of several factors, which are influenced mainly by heredity, age and gender. Lifestyle factors, such as diet or grooming habits appear to play a minimal role.

Some of the factors believed to contribute to the development of acne are:

• Hormonal levels: Certain hormones, particularly androgens, such as testosterone and dihydrotestosterone (DHT), promote acne. Of importance are not only absolute levels of these hormones but also the levels relative to other hormones, such as estrogens and progestins. Acne tends to flare up when levels of androgens increase either absolutely or relatively to other hormones. This is one of the main reasons why acne flare-ups are linked to puberty and menstrual cycles.
• Excessive sebum production: Excess sebum from overactive sebaceous glands is an important factor in acne. Excess sebum is most often caused by increase in absolute or relative levels of androgenic hormones (see above). Sebum production may also be increased by stress and heat.
• Stress: There is some preliminary evidence that stress may exacerbate acne. The proposed mechanisms of this effect include altered hormonal levels (such as CRH and adrenal hormones) and suppression of immune system linked to stress.
• Accumulation of dead skin cells: Excessive shedding of dead skin cells can plug the pore, creating a nutrient-rich anaerobic (oxygen-free) environment conducive to overgrowth of acne-causing bacteria.
• Bacteria: Bacteria are part of the normal microflora residing in pores. Under normal circumstances, the microflora is in balance with the environment of the pore and does not cause any problems. However, various factors can tip the balance and cause bacteria to grow excessively. This triggers inflammatory response leading the acne lesions. Propionibacterium acnes (P. acnes) is the species of bacteria most commonly associated with acne. However, other species may have a role as well. The factors contributing to the overgrowth of P. acnes include, excess sebum, accumulation of dead cell plugging the pore, suppression of immune system and others. Some people become allergic to P. acnes and may develop inflammatory acne lesions even when bacterial overgrowth is minimal.
• Skin irritation: Skin irritation does not generally cause acne by itself, but may induce a flare-up or exacerbate existing lesions.
• Drugs, pollutants: Certain drugs and environmental pollutants have been linked to acne with varying degree of certainty. Some examples include anabolic steroids, lithium, and barbiturates. Exposure to high levels of chlorine compounds, such as chlorinated dioxins, can cause severe, long-lasting acne, known as Chloracne.

Treatment

There is no cure for acne. However, there are a wide variety of treatments designed to keep acne under control - each addressing one or more factors contributing to the development of acne lesions. See Acne Treatments.