Causes of Acne

Acne is a long term skin disease. This disease is also known as Acne Vulgaris. Acne occurs when hair follicles are coggled with dead skin cells and oil from the skin.

There may be many risk factors for the development, but Genetics is only proven risk factor. Possible secondary risk factors are hormones, infections, diet, stress etc. 

Sunlight and cleanliness have no direct effect in Acne. Studies investigating the impact of smoking on the incidence and severity of acne have been inconclusive.

Hormonal Factor

Several hormones are associated with Acne. Main hormones are testosterone, androgen, growth hormones, dihydrotestosterone (DHT), dehydroepiandrosterone (DHEA), insulin-like growth factor 1 (IGF-1).   

Infections

It is widely suspected that a bacteria named P. acnes helps to develop acne. But how this anaerobic bacteria do the process is not well understood yet. 

Diet

Relationship between Acne and Diet is still unclear. But there are few evidence that shows the relationship between them. Taking exceeding doses of Vitamin B12 worsen existing acne. Few studies show that dairy milk consumption is positively associated with a higher frequency and severity of acne.

Stress

Connection between Acne and Stress are debated. But many high quality studies shows that stress causes or worsens the acne. 

Environmental Factors

Helmets, chinstraps and this type mechanical obstructions of skin follicles can worsen pre-existing acne. 

Medications

Several medications can worsen pre-existing acne, with examples being  lithium,  hydantoin,  isoniazid,  glucocorticoids,  iodides,  bromides, and  testosterone.

Genetic Factor

Genetic factors are associated with acne. XXY syndrome is associated with severe acne. According to wikipedia:

The predisposition to acne for specific individuals is likely explained by a genetic component, a theory which is supported by studies examining the rates of acne among twins and first-degree relatives. Severe acne may be associated with XYY syndrome. Acne susceptibility is likely due to the influence of multiple genes, as the disease does not follow a classic (Mendelian) inheritance pattern. Multiple gene candidates have been proposed including certain variations in tumor necrosis factor-alpha (TNF-alpha), IL-1 alpha, and CYP1A1 genes, among others. Increased risk is associated with the 308 G/A single nucleotide polymorphism variation in the gene for TNF.