Primary causes

The root cause of 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:

* Family/Genetic history. The tendency to develop acne runs in families. For example, school-age boys with acne often have other members in their family with acne as well. A family history of acne is associated with an earlier occurrence of acne and an increased number of retentional acne lesions.[11]
* Hormonal activity, such as menstrual cycles and puberty. During puberty, an increase in male sex hormones called androgens cause the glands to get larger and make more sebum.[12]
* Inflammation, skin irritation or scratching of any sort will activate inflammation. Anti-inflammatories are known to improve acne[citation needed].
* Stress, through increased output of hormones from the adrenal (stress) glands, although modern tests have said otherwise and point to this not being a cause[citation needed].
* Hyperactive sebaceous glands, secondary to the three hormone sources above.
* Accumulation of dead skin cells that block or cover pores[citation needed].
* Bacteria in the pores. Propionibacterium acnes (P. acnes) is the anaerobic bacterium that causes acne. In-vitro resistance of P. acnes to commonly used antibiotics has been increasing.[13]
* Use of anabolic steroids[citation needed].
* Any medication containing lithium, barbiturates or androgens.[citation needed]
* Exposure to certain chemical compounds. Chloracne is particularly linked to toxic exposure to dioxins, namely Chlorinated dioxins[citation needed].
* Exposure to halogens. Halogen acne is linked to exposure to halogens (e.g. iodides, chlorides, bromides, fluorides)[citation needed].
* Chronic use of amphetamines or other similar drugs.[14]

Several hormones have been linked to acne: the androgens testosterone, dihydrotestosterone (DHT) and dehydroepiandrosterone sulfate (DHEAS), as well as insulin-like growth factor 1 (IGF-I). In addition, acne-prone skin has been shown to be insulin resistant[citation needed].

Development of acne vulgaris in later years is uncommon, although this is the age group for Rosacea which may have similar appearances. True acne vulgaris in adult women may be a feature of an underlying condition such as pregnancy and disorders such as polycystic ovary syndrome or the rare Cushing's syndrome. Menopause-associated acne occurs as production of the natural anti-acne ovarian hormone estradiol fails at menopause. The lack of estradiol also causes thinning hair, hot flashes, thin skin, wrinkles, vaginal dryness, and predisposes to osteopenia and osteoporosis as well as triggering acne (known as acne climacterica in this situation).