acne causes

 

Causes

Risk factors for the development of acne, other than genetics, have not been conclusively identified. Possible secondary contributors include hormones, infections, diet, and stress. Studies investigating the impact of smoking on the incidence and severity of acne have been inconclusive.^[2][40][41] Sunlight and cleanliness are not associated with acne.^[14]

Genes

Acne appears to be highly heritable; genetics explain 81% of the variation in the population.^[15] Studies performed in affected twins and first-degree relatives further demonstrate the strongly inherited nature of acne.^[2][15] Acne susceptibility is likely due to the influence of multiple genes, as the disease does not follow a classic (Mendelian) inheritance pattern. These gene candidates include certain variations in tumor necrosis factor-alpha (TNF-alpha), IL-1 alpha, and CYP1A1 genes, among others.^[19] The 308 G/A single nucleotide polymorphism variation in the gene for TNF is associated with an increased risk for acne.^[42] Acne can be a feature of rare genetic disorders such as Apert's syndrome.^[15] Severe acne may be associated with XYY syndrome.^[43]

Hormones

Hormonal activity, such as occurs during menstrual cycles and puberty, may contribute to the formation of acne. During puberty, an increase in sex hormones called androgens causes the skin follicle glands to grow larger and make more oily sebum.^[12] The androgen hormones testosterone, dihydrotestosterone (DHT), and dehydroepiandrosterone (DHEA) are all linked to acne. High levels of growth hormone (GH) and insulin-like growth factor 1 (IGF-1) are also associated with worsened acne.^[44] Both androgens and IGF-1 seem to be essential for acne to occur, as acne does not develop in individuals with complete androgen insensitivity syndrome (CAIS) or Laron syndrome (insensitivity to GH, resulting in very low IGF-1 levels).^[45][46]

Medical conditions that commonly cause a high-androgen state, such as polycystic ovary syndrome, congenital adrenal hyperplasia, and androgen-secreting tumors, can cause acne in affected individuals.^[47][48] Conversely, people who lack androgenic hormones or are insensitive to the effects of androgens rarely have acne.^[47] Pregnancy can increase androgen levels, and consequently, oily sebum synthesis.^[48][49] Acne can be a side effect of testosterone replacement therapy or anabolic steroid use.^[1][50] Over-the-counter bodybuilding and dietary supplements often contain illegally added anabolic steroids.^[1][51]