Preventers control the swelling and inflammation in the airways, stopping them from being so sensitive and reducing the risk of severe attacks.

Not everyone with asthma will be prescribed preventer medicine.

The protective effect builds up over a period of time so they need to be taken every day (usually morning and evening) even when you are feeling well.

Preventers do not give immediate or quick relief when you are breathless but instead they reduce long-term inflammation. Preventer inhalers usually contain a low dose of steroid medicine.

There are several kinds of preventers, but they all work in the same way. You will be started on an appropriate level of treatment to get your symptoms under control; once this has been achieved the treatment will be reduced to the lowest possible dose.

Preventers are usually brown, red or orange inhalers.

When are preventers prescribed?

You should be prescribed a preventer if you:

• are breathless, cough or have a tight chest during everyday activities three or more times a week
• need to use your reliever inhaler three times a week or more
• have sleep disturbed by cough or chest tightness each week
• have bad attacks of breathlessness when you have a chest infection or are in a smoky atmosphere.

Once this protection is working, occasionally forgetting to take your inhaler will usually not have bad effects. But forgetting or stopping for several days at a time will mean your protection begins to disappear. If you stop using your preventer, chest infections are more likely to bring on an asthma attack.

Will my preventer medicines change?

Yes. It is likely that you will have to change your medicines from time to time.

If your asthma gets really bad, you may need to increase the dose you take. Or you may need a short course of steroid tablets as well as your regular preventer.

When you begin taking preventer medicine, your doctor or asthma nurse may want you to take a higher dose each day. This will get your asthma under control quickly. As your symptoms improve, you may be able to take fewer daily puffs or move to a lower strength inhaler

Side effects of preventer medicines

The possibility of side effects from taking your inhaled preventer medicine is very low. Because the inhaled medicine goes straight down to the airways where it is needed, very little is absorbed into the rest of the body.

If you use preventer medicine there is a small risk of having a sore tongue, sore throat, hoarseness of the voice and a mouth infection called thrush. To help prevent these side effects, rinse your mouth out and brush your teeth after using your preventer inhaler. Using a spacer will also help reduce the possibility of thrush.

Children should be monitored closely if they are taking preventer medicines - especially for growth.

It is possible that long-term and high-dose use of preventer medicines (inhaled steroids) may cause some other side effects (See 'Side effects of long-term use of steroid tablets', below). That is why your doctor and asthma nurse will try to keep you on the lowest dose to control your symptoms.

Several studies have suggested the possibility of a very slight increased risk of the development of cataracts in elderly people who have used inhaled steroids. As with use of all medicines, careful attention needs to be paid to the risk versus benefit argument and it's as likely that any risk can be reduced by always using the lowest possible dose of medication to control the condition.