What causes acne?
What is acne?
Acne is a common chronic inflammatory skin condition that involves the pilosebaceous unit (hair follicles and oil glands). A variety of spots appear on the face, neck, shoulders, chest and back.
- Inflamed papules and pustules are commonly called spots, pimples and zits.
- Dark- or skin-coloured papules are comedones. These are better known as blackheads and whiteheads.
- Acne can lead to secondary skin colour changes (red, white and brown patches) and scarring.
The most common type of acne is acne vulgaris.
Acne is most prevalent in those aged 16 to 18 years. It may have profound social and psychological effects, particularly during puberty and adolescence, when physical appearance and fitting in with one's peers are particularly important.
Why is acne often most severe during teenage years?
The precise reasons that acne is most severe during the teenage years are being studied. There are several theories.
There are higher levels of sex hormones after puberty than in younger children.
- Sex hormones are converted in the skin to dihydrotestosterone (DHT), which stimulates sebaceous (oil) glands at the base of hair follicles to enlarge.
- The sebaceous glands produce sebum. Changes in sebum composition may lead to acne lesions.
- The activated sebaceous gland cells (sebocytes) also produce proinflammatory factors, including lipid peroxides, cytokines, peptidases and neuropeptides.
- Hair follicles are tiny canals that open into skin pores (tiny holes) on the skin surface. The follicles normally carry sebum and keratin (scale) from dead skin cells to the surface. Inflammation and debris leads to blockage of the skin pores – forming comedones.
- The wall of the follicle may then rupture, increasing an inflammatory response.
- Bacteria within the hair follicle may enhance inflammatory lesions.
While acne is most common in adolescents, acne can affect people of all ages and all races. It 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. It may also start in adult life.
Why is acne worse in some people?
Some people have particularly severe acne. This may be because of:
- Genetic factors (family members have bad acne)
- Hormonal factors (higher levels of male/androgenic hormones) due to:
- Polycystic ovaries (common). Hyperinsulinaemia and insulin resistance are characteristically found in women with polycystic ovarian syndrome, who are prone to acne among other problems
- Psychological stress and depression
- Excessive corticosteroids eg Cushing disease (rare)
- Enzyme deficiency eg sterol hydroxylase deficiency (very rare)
- Environmental factors such as:
- High humidity causing swelling of the skin
- Cosmetics especially certain moisturisers, foundation and pomades. Watch out for products that contain lanolin, petrolatum, vegetable oils, butyl stearate, lauryl alcohol and oleic acid.
- Pressure from headbands and chin straps (eg "fiddler's neck", a condition seen in violin or viola players, where continual pressure from the violin against the neck causes skin irritation)
- Excessive dairy products, meat protein and sugars in the diet. Diets low in zinc or high in iodine can worsen pustular acne.
- Certain medications may provoke acne.
- Much of the individual variation in acne severity is due to variation in the innate immune system and the production of inflammatory mediators such as cytokines, defensins, peptidases, sebum lipids, and neuropeptides. Evidence has emerged that inflammation leads to distension and occlusion of the hair follicle, which then ruptures.
Do certain foods cause acne?
Some studies suggest there is a link between the food we eat and acne. It is very difficult to study the role of diet and acne.
Acne is reported to be less common in people that have a diet with lower glycaemic index, eg, natives from Kitava and Papua New Guinea, the 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 that tends to peak at the time of full maturity (age 16 to 18).
Several studies, criticised for their quality, have shown benefits in acne from a low-glycaemic, low-protein, low-fat and low-dairy diet. The reasons for these benefits are thought to relate to the effects of these foods on insulin and insulin-like growth factor-1 (IGF-1).
Insulin induces male hormones (androgens), glucocorticoids and growth factors. These provoke keratinisation (scaling) of the hair follicle and sebum production. An increase in sebum production and keratinisation is a factor in the appearance of acne.
Foods that increase insulin production
Foods that increase insulin levels have a high glycaemic index. The glycaemic index is a measurement of how carbohydrates have an effect on our blood sugar levels. When we eat foods with a high glycaemic index, such as white bread and baked goods, our blood sugar level rises. This increases the amount of insulin produced in our body.
Although cow's milk has a low glycaemic index, it contains androgens, oestrogen, progesterone and glucocorticoids, which also provoke keratinisation and sebum production. Milk also contains amino acids (eg arginine, leucine, and phenylalanine) that produce insulin when combined with carbohydrates. Other components of milk that might induce comedones include whey proteins and iodine.
Caffeine, theobromine, and serotonin found in chocolate may also increase insulin production.
Food containing fatty acids
Fatty acids are needed to form sebum. Studies show that some monounsaturated fatty-acids, such as sapienic acid and some vegetable oils, can increase sebum production. However, the essential fatty acids linoleic, linolenic and gamma linolenic acid can unblock the follicles and reduce sebum production.
Suitable food if you have acne
Some people with acne have reported improvement in their skin when they follow a low-glycaemic index diet and increase their consumption of whole grains, fresh fruits and vegetables, fish, olive oil, garlic, while keeping their wine consumption moderate.
It’s a good idea to drink less milk and eat less of high glycaemic index foods such as sugar, biscuits, cakes, ice creams and bottled drinks. Reducing your intake of meat and amino acid supplements may also help.
Seek medical help if you are concerned about your skin, as changing diet does not always help.
Why does acne eventually clear up?
We do not understand why acne eventually clears up. It does not always 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 or to the activity of the immune system.