What causes acne? : Acne Treatment Guide

Acne is caused by a combination of the following:

  • Excess sebum production (oily skin)
  • Clogged up sebaceous glands and skin pores
  • Bacteria
  • Inflammation

Excess sebum production

The skin is comprised of three layers, one of these being the dermis which contains thousands of tiny glands called sebaceous glands. These glands are responsible for the secretion of oil called sebum which helps to moisten the skin and hair follicles. It does so via millions of tiny pores within the skin. The sebaceous glands are affected by the hormone testosterone: this hormone occurs in both men and women and controls the amount of sebum produced. But these glands can produce excess amounts of sebum – usually during adolescence which is due to rising levels of testosterone. Boys have higher levels of testosterone than girls which mean that they are more likely to develop acne. Boys also produce greater amounts of oil due to their larger sebaceous glands which is a cause of acne.

Too much oil in your skin will result in greasy looking skin which is also a fertile breeding ground for acne.

Note: hair follicles are located in the subcutaneous layer of skin which lies beneath the dermis.

Learn more about how the skin works in your skin section of this guide.

Clogged up sebaceous glands

Over-production of sebum then clogs up the sebaceous glands and the skin pores. This coincides with the failure of dead skin cells to be shed properly which then block the openings to the hair follicles. The sebaceous glands enlarge to form a spot or pimple.

This results in a build up of oil within the hair follicles.


We all have a type of ‘acne bacteria’ which lives on our skin but doesn’tusually cause any problems. In other words it does not lead to acne unless something happens to trigger this such as excessive oil production.

But if you are prone to acne then this build up of oil plus your own susceptibility will combine to produce an ideal breeding ground for acne. Bacteria will flourish in this environment to produce those all too familiar spots and pimples.

This bacterium is known as ‘Propionibacterium Acnes’or ‘P acnes’for short.


These bacteria multiply which results in painful swellings beneath these spots - known as an inflammation. This soreness may be caused by chemicals produced by the bacteria which trigger an inflammatory reaction by the body’s immune system.

Acne overview

So, basically acne develops when too much oil (sebum) is produced from sebaceous glands within hair follicles, often due to an increase in testosterone levels. This abnormal reaction affects the process in which dead skin cells are shed which causes them to block the secretion of oil from the sebaceous glands.

This results in blocked skin pores and enlarged sebaceous glands which lead to the formation of pimples or spots. If these spots come in contact with the air, this can cause them to change to a black colour or become a ‘blackhead’.

Those which are not exposed to the air remain as ‘whiteheads’.These can become red and swollen due to the presence of bacteria on the surface of the skin. These bacteria actively thrive in the sebum and then multiply in the sebaceous gland which results in an angry red or inflamed appearance on the skin.

In severe cases the clogged up hair follicle ruptures which causes the inflamed acne to spread. This then develops into cysts which can result in scarring.

Find out about acne symptoms.

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