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.

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.