Causes of acne

Most people develop acne during adolescence. It is most prevalent in those aged 16 to 18 years. The reasons are:

• There are higher levels of sex hormones at puberty than in younger children.
• These hormones are converted in the skin to dihydrotestosterone (DHT) which stimulates oil glands to enlarge.
• The oil glands, called sebaceous glands, produce sebum. The more sebum, the more likely it is that acne will be troublesome.
• If sebum and keratin (dead skin cells) block the skin pores, comedones can develop.
• The wall of the follicles may rupture.
• Bacteria and comedonal debris cause acne pimples or pustules (inflammatory lesions).

Acne usually becomes less of a problem after the age of 25 years, although about 15% of women and 5% of men continue to have acne as adults.

Aggravating factors

Some people have particularly severe acne. This may be because of:

• Genetic factors (family members have bad acne)
• Hormonal factors (higher levels of androgenic hormones) due to:
  • Polycystic ovaries (common)
  • Enzyme deficiency eg sterol hydroxylase deficiency (very rare)
  • Excessive corticosteroids (eg Cushing's disease) (rare)
  • Psychological stress and depression
• Environmental factors such as:
  • High humidity causing swelling of the skin
  • Cosmetics especially certain moisturisers, foundation and pomades (watch out for lanolin, petrolatum, vegetable oils, butyl stearate, lauryl alcohol and oleic acid)
  • Petroleum oils
  • Pressure from headbands & chin straps (eg: "fiddler's neck")
  • Dietary factors such as excessive dairy products (controversial). A study published in 2007 in male adults with acne has shown benefits from a low glycaemic diet.
• Certain medications.

More about diet and acne

It is possible that diet may influence the development of acne in some individuals. Western diets include frequent consumption of carbohydrates with high glycaemic index (sugar), which increase the amount of insulin circulating in the blood. The caffeine, theobromine, and serotonin in chocolate may also increase insulin production. Insulin induces more male hormones (androgens), glucocorticoids and growth factors, which provoke keratinisation (scale) of the hair follicle and sebum production (skin oil). Comedones are the result of occlusion of the follicle by scale and sebum. Hyperinsulinaemia and insulin resistance are characteristically found in women with polycystic ovarian syndrome, who are prone to acne among other problems.

Although cow's milk has a low glycaemic index, it also contains additional androgens, oestrogen, progesterone and glucocorticoids. Other components of milk that might induce comedones include whey proteins and iodine. Milk contains amino acids (eg, arginine, leucine, and phenylalanine) that produce insulin when combined with carbohydrates.

Fatty acids are needed to form sebum; it has been found that monounsaturated fatty-acids such as sapienic acid and some vegetable oils can increase sebum production, and the essential fatty acids linoleic, linolenic and gamma linolenic acid can unblock the follicles and reduce sebum production.

Diets low in zinc or high in iodine can worsen pustular acne.

Acne is reported to be uncommon in peoples that have a diet with lower glycaemic index as in the case in natives from Kitava and Papua New Guinea, Ache people of Paraguay, Inuits and rural residents of Kenya, Zambia and Bantu. These people tend to become sexually mature at a later age than in the cities where higher glycaemic index foods are consumed. Early puberty is associated with earlier onset and more severe acne, which tends to peak at the time of full maturity (age 16 to 18).

Suitable food if you have acne

Some people with acne have reported improvement by following a low-glycaemic index diet and increasing whole grains, fresh fruits and vegetables, fish, olive oil, garlic, and moderate wine consumption.

It is reasonable to minimise milk and high glycaemic index foods such as sugar, biscuits, cakes, ice creams and bottled drinks. However, seek medical help if you are concerned about your skin as changing diet does not always help.

Why does acne eventually clear up?

Why acne eventually resolves is not understood. It does not coincide with a reduction in sebum production or with a reduction in the number of bacteria. It may relate to changes in the sebaceous glands themselves.