Acne is the most common skin disorder in the United States, affecting more than 17 million Americans. Most adolescents in Western countries experience some degree of acne, which generally resolves as sex hormone concentrations decline with time. Some cases, however, persist into adulthood or begin in adulthood.

Common acne, as it appears in adolescents, is associated with many factors, including genetics, hormonal abnormalities, and clogged skin follicles. Increased production of sex hormones during puberty leads to growth of the skin glands and increased lubrication of the skin, which is optimal for bacterial growth. Under these conditions, the Propionibacterium acnes bacteria grows and causes inflammation that results in the characteristic acne appearance.

Acne most commonly affects areas of the body with the greatest number of skin glands. These include the face, upper back, neck, chest, and upper arms. Scarring can also occur, particularly in individuals with darker complexions.

Risk Factors

• Cosmetics: Skin and hair products that contain oils or dyes can exacerbate acne lesions. Water-based cosmetics are less likely to cause acne.
• Repetitive skin trauma: Rubbing (even with cleansing agents), scrubbing, or restrictive clothing (e.g., bra straps, helmets, turtlenecks) can worsen acne.
• Environmental exposures: Humidity and sweating can worsen acne. Exposure to certain chemicals (e.g., dioxin and other halogenated hydrocarbons) that are found in herbicides and other industrial products can cause severe acne and scarring.
• Drugs: Certain drugs are likely to cause acne, including steroids, phenytoin, isoniazid, disulfiram, lithium, and B vitamins.
• Diet: Western diets, and milk in particular, have been linked to acne (see Nutritional Considerations).
• Climate: Humidity and heavy sweating may lead to acne.
• Genetics: Genetics likely play a role in the manifestation of acne, especially in persistent and late-onset cases.
• Stress: Stress is believed to be associated with acne exacerbations, but further study is required to establish this connection.

Acne Vulgaris: Diagnosis and Treatment

Diagnosis

• A medical history and dermatologic examination are necessary to characterize the types of acne and to evaluate underlying medical disorders.

Treatment

Treatment should address both the physical and psychological effects of acne. Light and laser therapies may be used to treat acne in the future.

• A number of topical therapies are used to treat acne, including retinoids (e.g., tretinoin, adapalene and tazarotene), acid preparations (e.g., salicylic acid, azelaic acid and glycolic acid), and benzoyl peroxide.
  
• Severe acne can be treated with intensive topical treatment, but may require oral medications.
  
  Oral antibiotics can be used to attack the bacteria that cause acne. They are usually prescribed for six months.
  
  Isotretinoin (Accutane) is usually reserved for the most severe cases of acne that do not improve with other treatments. It is effective, but it is also expensive and has many potential adverse effects, including birth defects if pregnancy occurs. Close follow-up is necessary for laboratory work, including pregnancy tests, liver function tests, cholesterol levels, and blood counts. Treatment usually lasts six months.

Acne Vulgaris: Nutritional Considerations

Some studies suggest that acne occurs more commonly in countries following Westernized diets. However, the role of nutritional factors remains unclear. For years, dermatologists advised people to avoid chocolate, fried foods, and fatty foods, although proof of their role was lacking. Acne may not be worse in individuals with a higher intake of table sugar or chocolate.

Recent evidence suggests that diet may indeed contribute to hormone-related acne. In population studies, the following factors are associated with acne:

Western diets and acne: Indigenous populations that eat plant-based diets composed mainly (roughly 70 percent) of unprocessed or minimally processed foods high in carbohydrate and fiber, and emphasizing unsaturated, rather than saturated, fats (tubers, fruit, vegetables, peanuts, corn, and rice), are largely free of acne. In contrast, the vast majority of teenagers and 40 to 54 percent of the adult population in Western societies have some degree of facial acne.

Evidence also suggests that, as immigrants begin a typical Western diet, their previously low incidence of acne rises to the levels found in Western societies. Aspects of diet under particular scrutiny are as follows:

• Dietary fat contributes to acne production, and excesses of both fat and carbohydrate contribute to increased fat secretion in human skin. In contrast, restricting calories can reduce acne production by as much as 40 percent.
  
  Diets high in saturated fat, meat, and milk increase blood concentrations of insulin-like growth factor (IGF-I), which, in turn, stimulates the production of sex hormones that increase acne production. Plant-based diets, low-fat diets, high-fiber diets, and vegetarian diets reduce levels of IGF-I.
• Dairy products may play a role in acne. In the Nurses Health Study II, more than 47,000 women completed questionnaires based on recalling their diet during high school, and associations were estimated between various food groups and diagnosis of teenage acne. Women who reported having consumed more than two glasses of skim milk per day during their teen years (ages 13 to 18) had a 40 percent greater prevalence of teenage acne, compared with those drinking less than one glass per week.

While mechanisms that might explain the association have not been established, several possibilities have been suggested. Milk contains both hormones and hormone-like chemicals (e.g., IGF-I) that may survive processing and affect the skin glands. Apart from the hormones found in milk, hormones or growth factors may be produced in the human body in response to milk ingestion. For instance, regular milk ingestion by adults is associated with an elevation of blood IGF-I concentrations.