Causes of acne
Exactly why some people get acne and some do not is not fully known. It is known to be partly hereditary. Several factors are known to be linked to acne:
  • Stress
  • Hormonal activity
  • Hyperactive sebaceous glands
  • Accumulation of dead skin cells
  • Bacteria in the pores
  • Skin irritation or scratching of any sort
  • Anabolic steroids
  • Any medication containing halogens (iodides, chlorides, bromides), lithium, barbiturates, or androgens
  • Exposure to high levels of chlorine compounds, particularly chlorinated dioxins, can cause severe, long-lasting acne, known as Chloracne
Traditionally, attention has focused mostly on over-production of sebum as the main contributing factor of acne. More recently, more attention has been given to narrowing of the follicle channel as a second main contributing factor. Abnormal shedding of the cells lining the follicle, abnormal cell binding ("hyperkeratinization") within the follicle, and water retention in the skin (swelling the skin and so pressing the follicles shut) have all been put forward as mechanisms involved, but there does not appear to be much conclusive medical research on the subject.

Acne misconceptions
Since the medical knowledge about acne is still relatively small, there are many misconceptions and rumours about what causes the condition:
  • Diet. Chocolate, potato chips and sugar, among others, have not been shown to affect acne. This means that the scientific studies done to date did not find a statistically significant difference between acne in two groups of people, one group eating the food in question and one group avoiding it. However, one recent study [1], based on a survey of 47,335 women, did find a positive association between milk consumption and acne. The researchers hypothesize that the association may be caused by the hormones in milk. Seafood, on the other hand, may contain relatively high levels of iodine, but probably not enough to cause an acne outbreak. Still, people who are prone to acne may want to avoid excessive consumption of foods high in iodine.
  • Deficient personal hygiene. Acne is not caused by dirt. This misconception probably comes from the fact that acne involves skin infections. In fact the blockages that cause acne usually occur deep within the narrow follicle channel, where it is usually impossible to wash them away, from the cells and sebum created there by the body. The bacteria involved are the same bacteria that are always present on the skin. It is advisable to clean the skin on a regular basis, but doing so will not prevent acne. Anything beyond very gentle cleansing can actually worsen existing lesions and even encourage new ones by damaging or overdrying skin.