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Acne is just another word for pimples. If you have severe acne, you get lots of pimples, or pimples that are large, red and sore.

Most people don't like it when they get pimples on their face. Acne can also affect other parts of your body. You can get it on your neck, chest, back and arms.

Pimples happen when you get a build up of natural oil under your skin. Small glands in your skin make an oily substance called sebum. This stops your skin from drying out.

Sebum comes out onto the surface of your skin through tiny holes called pores.

If a pore gets blocked, sebum can build up. This can cause several kinds of swellings or pimples on your skin.

• If sebum builds up just under your skin, you get white bumps called whiteheads.
• Blocked pores can get quite wide and open up. This causes small dark marks called blackheads.
• Pimples can turn red and inflamed. These are called papules. They happen if bacteria start growing in the sebum that's built up.
• Some inflamed pimples contain pus. These are called pustules.

Pimples can go deep in your skin and become painful.¹

Very bad pimples can cause scars as they heal.²

We don't know exactly what causes acne.

The main reason teenagers get acne is probably the change in hormones that happens when you reach puberty.³ The change in hormones can cause your skin to make more sebum (oil). The extra sebum can make your skin greasy.

You're more likely to have acne if other people in your family have it.⁴ And some kinds of oily make-up may block your pores and trigger acne.⁴

If you have acne, there are things that can make it worse:⁴

• Rubbing your skin
• Picking or squeezing your pimples
• Tight clothes or bag straps that rub your skin
• Pollution and high humidity
• If you're female, the change in your hormones that happens when you have your periods, or when you start or stop taking birth control pills.

There are lots of myths about acne. Here are some of the things that you may hear.^{4 5}

You get acne when you don't wash enough

• This isn't true. Blackheads aren't black because of dirt. Hard scrubbing can make acne worse.

Greasy foods cause acne

• There's no good evidence that eating fatty foods or chocolate causes acne for most people.

You can catch acne

• Again, this isn't true. You can't catch acne or pass it on to someone else. Although acne is partly caused by bacteria, these live on your skin naturally and are usually harmless.

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.