To understand what causes acne, we must first understand what acne is.
Acne is a disease of a pilosebaceous unit (mini-organ in skin where hair is formed – see picture). The pilosebaceous unit consists of the hair shaft, hair follicle, sebaceous gland (which secretes oil or sebum to keep the skin moisturised), and a tiny muscle (erector pili muscle) which makes the hair stand on end when it contracts.

The hair follicle (pore) is lined with epithelial cells that produce keratin. New cells are produced almost every 24 days. The dead cells are excreted through the follicular opening. Both the hair follicle and the sebaceous gland open into a common duct that opens on the surface of the skin. This is called a pilosebaceous duct. In the pilosebaceous unit there is a bacterium called Propionibacterium acnes and we all have this bacterium.

Various factors determine whether you have an acne-prone skin or not and many of these factors are linked. The following factors can therefore lead to the development of acne:

  • Your genes or DNA
  • Blocked pilosebaceous ducts (see picture)
  • The growth of the bacteria normally found in the pilosebaceous unit
  • Sebaceous glands activated by hormones that are secreted in the blood and reach the skin receptors
  • External factors such as oily cosmetics, hair products, medications like oral or topical steroids, smoking and diet.
  • Acne is mostly determined by your genes

It is important to know that your genes or DNA play the biggest role in acne formation. That is why acne often runs in families.
Your genes control how much keratin your cells produce and how much oil your sebaceous glands secrete. Your genes also determine how much hormones (testosterone and DHT) your body produces, which, in turn, cause the sebaceous glands to enlarge and overproduce oil.
How does acne form?

Acne forms when the cells that line the hair follicles overproduce keratin, which makes the dead skin that is usually excreted via the pilosebaceous duct, clump together and block the pilosebaceous unit. An overproduction of oil by the sebaceous gland can, together with the clumps of cells, block the sebaceous unit. When pilosebaceous units are blocked, comedones (small bumps or clogged hair follicles) form that can either be opened (blackheads) or closed by skin (whiteheads).

When the unit is blocked, the bacterium found in the pilosebaceous unit grows and releases pro-inflammatory markers that lead to inflammation. This causes red pimples with pus. The follicle will then expand as a result of the blockage in the pilosebaceous unit. However, when the follicle ruptures into the surrounding skin, especially when a pimple is squeezed, it can lead to more inflammation and bigger pustules and nodules.