However, men and women in their 30s and 40s can also suffer. There are many treatments available to help deal with the condition.

What is acne?
Acne is a skin condition that typically causes one or more of the following:

- blackheads (comedones)
- whiteheads
- red or yellow spots
- greasy skin
- scars

Acne typically affects the skin of the face, back, neck, chest and arms and the severity of the condition can vary.

Acne affects people of all skin colours. The processes that cause acne are exactly the same in people with black or brown skin but the impact is altered by the skin pigmentation.

Acne is very common and affects about 80 in 100 people aged 11-30 at some time.

The skin
The surface of the skin has lots of small sebaceous glands just below the surface. These glands make an oily substance called sebum that keeps the skin smooth and supple.

Tiny pores (holes in the skin) allow the sebum to come to the skin surface. Hairs also grow through these pores.


What causes acne?
Acne is caused by the overactivity of the sebaceous glands that secrete oily substances onto the skin.

The sebaceous glands of people with acne are especially sensitive to normal blood levels of a hormone called testosterone, found naturally in both men and women.

Testosterone in people prone to acne triggers the sebaceous glands to produce an excess of sebum. At the same time, the dead skin cells lining the openings of the hair follicles (the tubes that hold the hair) are not shed properly and clog up the follicles.

These two effects combined cause a build-up of oil in the hair follicles. This causes blackheads and whiteheads to form.

For some people, their acne does not progress beyond this stage.

However in other people, the build-up of oil in the hair follicles creates an ideal environment for a bacterium called Propionibacterium acnes to grow.

These bacteria normally live harmlessly on your skin but when this ideal environment is created, they grow. They feed off the sebum and produce substances that cause a response from your body's immune system. This inflames the skin and creates the redness associated with spots.

In more severe 'inflammatory acne', cysts develop beneath the skin's surface. These acne cysts can rupture, spreading the infection into nearby skin tissue. This can result in scarring.


Acne myths
Contrary to popular belief acne is not caused by:

- eating fatty food or chocolate1
- dirt - blackheads get their dark colour through excess skin pigment - not dirt so washing more does not help, although if you do not wash your skin at all, bacteria will be able to multiply.

Acne is not contagious, so you cannot catch it.

What makes acne worse?
There are a number of things that can make your acne worse. These include the following:

- picking and squeezing the spots may cause further inflammation and scarring
- stress can make acne worse in some people, although it is not clear why in women, outbreaks may be affected by the hormonal changes that occur during the menstrual cycle1
- excessive production of male hormones such as testosterone from conditions such as polycystic ovary syndrome may be another cause.

- Some contraceptive pills may make acne worse. This is due to the type of progestogen hormone in some pills whereas some other types of contraceptive pills can improve acne. Your GP will advise you which contraceptive pill to take

- Some medicines can make acne worse. For example, some medicines taken for epilepsy, and steroid creams and ointments that are used for eczema. Do not stop a prescribed medicine if you suspect it is making your acne worse, but tell your GP. An alternative may be an option.

- Steroids can cause acne as a side-effect


Diagnosing acne
Acne is easily recognised by the appearance of the spots, and by their distribution on the body.

There are several varieties of acne and your doctor will be able to tell you which type you have after examining your skin.