Benzoyl peroxide is used to treat acne. It works as an antiseptic to reduce the number of germs (bacteria) on the surface of your skin.

It comes as a gel or face wash containing 5% benzoyl peroxide. This is available to buy from pharmacies under the brand name Acnecide.

Benzoyl peroxide is sometimes mixed with potassium hydroxyquinoline sulfate. This is an "antimicrobial" ingredient that kills micro-organisms on your skin. It's sold in pharmacies as Quinoderm cream.

Some benzoyl peroxide products are available on prescription only. This is because they contain other active ingredients such as antibiotics or retinoids (exfoliants).

Many popular skincare brands also make products that contain benzoyl peroxide, but at a lower strength. These are available to buy in pharmacies, supermarkets and shops. Brands include Clean & Clear, Neutrogena and Clearasil.

• Benzoyl peroxide 5% takes around 4 weeks to start working.
• You'll usually use it 1 or 2 times a day.
• The most common side effect is skin irritation. It is better to use it less often at first, then build up as your skin gets used to it.
• Pharmacy brands include Acnecide 5% gel and Acnecide Wash 5%.
• Benzoyl peroxide is also an ingredient in Duac Once Daily (with clindamycin, an antibiotic) and Epiduo gel (with adapalene, a retinoid).

Most adults and children over 12 years old can use benzoyl peroxide.

Benzoyl peroxide is not suitable for some people.

To make sure benzoyl peroxide is safe for you, tell your doctor before using this medicine if you:

• are allergic to benzoyl peroxide or other medicines.
• have damaged or broken skin where you need to use the treatment.
• have very bad acne with nodules (large, hard lumps that build up beneath the surface of the skin and can be painful) or cysts (large, pus-filled lumps that look similar to boils). These need to be treated by a doctor to avoid scarring.

Benzoyl peroxide is for use on your skin only.

Always wash your hands before and after using this medicine.

If your skin becomes dry or starts peeling, try using benzoyl peroxide less often. Put it on once a day or once every 2 days, until your skin gets used to it.

Benzoyl peroxide can bleach or discolour your hair, as well as clothes, towels and bedding. Keep it away from hair and coloured fabrics.

How to use benzoyl peroxide 5% gel

1. Wash the affected area with a mild skin cleanser and water.
2. Gently pat your skin dry.
3. Put a thin layer of gel on all the affected areas. If your whole face has acne, use a strip of gel (2.5cm long) each time.

You'll usually use the gel once or twice a day. If you have sensitive skin, use the gel once a day, before going to bed.

Try to avoid strong sunlight while using benzoyl peroxide gel. Use an oil-free sunscreen, or a moisturiser or foundation with added SPF30. In stronger sunlight, use SPF30 or above. Ask a pharmacist to help you pick a sunscreen that's right for your skin type.

How to use benzoyl peroxide 5% wash

1. Wet the area you want to treat.
2. Place a small amount of the product onto your hands.
3. Smooth it onto the affected area.
4. Keep the wash on your skin for no more than 1 to 2 minutes.
5. Rinse your face thoroughly with water.
6. Gently pat your skin dry.

You'll usually use the wash 1 or 2 times a day.

How long will I use it for?

It depends on how quickly your condition improves.

Benzoyl peroxide will usually start to work within 4 weeks, but once your acne is under control you may want to keep using it to stop your acne coming back.

What if I forget to use it?

It does not matter if you forget to use benzoyl peroxide.

When you remember, start using it again once or twice a day in the same way as before.

What if I use too much?

If you use too much benzoyl peroxide, your skin may become irritated. Wash off as much as you can and wait for the irritation to go away.

When your skin has calmed down again, you can start using benzoyl peroxide again. Be careful to follow the instructions on the package.

Like all medicines, benzoyl peroxide can cause side effects, although not everyone gets them.

Common side effects

These common side effects happen in more than 1 in 10 people. Talk to a doctor or pharmacist if these side effects bother you or do not go away:

• dry skin
• red or peeling skin
• burning or stinging (skin irritation)

Serious side effects

These serious side effects are rare and happen in less than 1 in 1,000 people. Stop using benzoyl peroxide if:

• the skin that you're treating becomes swollen
• you get blisters on your skin

If your symptoms do not get better within a couple of days or if they get worse at any time, contact a doctor straight away.

Serious allergic reaction

In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to benzoyl peroxide.

These are not all the side effects of benzoyl peroxide. For a full list, see the leaflet inside your medicine packet.

What to do about:

• dry skin – apply a moisturiser and lip balm regularly (the best type of moisturiser is an oil-free face moisturiser for sensitive skin). Try to take shorter showers, using warm water rather than hot.
• red or peeling skin – try using the gel or wash less often, or stop using it for a few days until the irritation goes away, then start again. Do not use other products on your skin in the meantime. Speak to a doctor if your symptoms do not get better or are severe.
• burning or stinging (skin irritation) – try using the gel or wash less often (once a day instead of twice, or every other day). It might help to stop using the gel for a few days until the irritation goes away, then start again. If the irritation does not go away after this time, stop using it and speak to a doctor.

It's usually safe to use benzoyl peroxide during pregnancy and while breastfeeding.

Benzoyl peroxide and breastfeeding

Although it's generally OK to use benzoyl peroxide when you're breastfeeding, do not use it on your chest area and wash your hands before touching your baby. This is so your baby does not come into contact with it.

Some products and medicines can irritate your skin if you use them while you're treating your skin with benzoyl peroxide gel or wash.

Do not use benzoyl peroxide with any other medicines that may have drying or irritating effects on your skin. These include alcohol-based skincare products. Always check the ingredients on the label and choose products for sensitive skin.

Do not use other benzoyl peroxide products or other acne medicines (such as isotretinoin), unless your doctor or pharmacist says it's OK. It may cause your skin to become very sore.

Mixing benzoyl peroxide with herbal remedies and supplements

There's very little information about taking herbal remedies and supplements while using benzoyl peroxide.