Asthma is a disease of the airways in the lungs. Its symptoms are caused by inflammation, which makes the airways red, swollen, narrower and extra-sensitive to irritants. This leads to recurrent attacks of wheezing, breathlessness, chest tightness and coughing. Mild attacks can settle down without treatment, but treatment usually helps them to resolve more quickly. Appropriate treatment can also reduce the risk of further attacks. If you experience a serious attack you should seek emergency help.

Asthma is a long-term (chronic) disease. Your asthma does not stay the same, but changes over time, and every person with asthma has good and bad days (or longer periods of time).

Asthma is very common. Around one out of every ten people in the Western World develops asthma at some stage in their life.

Inflammation of the airways causes asthma symptoms (wheezing, breathlessness, chest tightness and coughing) by restricting or limiting the airflow to and from the lungs. It does this by causing:

• swelling of the airways, which makes them narrower

• tightening of the muscles that surround the airways (also called bronchoconstriction), which makes them even narrower

• the production of too much mucus, which can plug up or block the airways

• longer-term damage to the walls of the airways, which prevents them from opening as widely as a normal airway.

When the airways have been inflamed for a long time, they become extra-sensitive. This means that they react faster and more strongly to various triggers, such as allergens, viruses, dust, smoke and stress.

Inflammation is a reaction to infections and other triggers in the lining of the airways and the underlying tissue. The inflammation makes the airways become red, swollen, narrower and extra-sensitive.

Asthma can start at any age, although about half of all people with asthma have had their first symptoms by the age of 10, and many children with asthma have had their first asthma attack before the age of 6.

The causes of asthma are not fully understood. Its symptoms are caused by inflammation, which makes the airways red, swollen, narrower and extra-sensitive to irritants. Asthma is probably usually caused by a mixture of hereditary factors (those you are born with) and environmental factors, but how these factors work together is still largely unknown.

Allergens from house dust mites and pets are the most common causes, but many other allergens, such as pollen and moulds, can cause asthma. Some people with asthma have no obvious allergies.

Asthma triggers are factors that start asthma symptoms or an asthma attack by irritating the airways or worsening the inflammation in the airways. These triggers can provoke attacks in individuals who already have a tendency to asthma, but they are not necessarily part of the cause of that tendency. The following triggers can cause asthma symptoms or start an asthma attack:

• infections, usually those caused by a virus (e.g. colds or flu)

• allergens, most commonly from house dust mites, pets or pollen

• exercise, especially in cold weather

• emotions, such as excitement, fear or anger

• irritants, such as air pollution

• smoking people with asthma and the parents of asthmatic children should avoid smoking

• changes in the weather (e.g. a cold spell)

• pressure on chest

• food additives, such as tartrazine (an artificial food colouring), or food allergens, such as peanuts (sensitised or allergic individuals can have a very severe allergic reaction).

• certain medications some people may be allergic to some drugs (e.g. aspirin).

When the airways have been inflamed for a long time, they become extra-sensitive. This means that they react faster and more strongly to various triggers, such as allergens, viruses, dust, smoke and stress.

Different triggers can start an asthma attack and people differ a lot in how easily and how severely they react. Some triggers (also called inciters) only cause tightening of the airways (bronchoconstriction) that lasts for just a short time. These triggers include:

• exercise

• cigarette smoke

• changes in air temperature

• laughing

• strong smells

Other triggers (also called inducers) also increase the underlying inflammation of the airways, and may have longer-term effects. Such triggers include:

• allergens (e.g. pets, house dust mites and pollen)

• infections (e.g. colds, flu)

• certain chemicals

Asthma symptoms typically come and go. You have trouble breathing, your chest feels tight and you can hear wheezing when you breathe or cough. These symptoms often occur during exercise or during the night.

An asthma attack is when your symptoms rapidly become more severe, usually rather suddenly. During an asthma attack, you have more trouble breathing.

You may get used to the asthma symptoms and not realise that your airflow is impaired and could be improved by treatment.

When your asthma is under good control, the airways are clear and air flows easily in and out.

Some causes and triggers are common to all people with asthma, and some are more individual, especially allergens. There are very big differences between people in how readily and how severely they react to different triggers. The severity of the symptoms can differ in the same person at different times, and the effects of treatment can also vary.

Your asthma does not stay the same, but changes over time, and every person with asthma has good days and bad days (or longer periods). However, if asthma is properly treated, there can also be long periods without symptoms or attacks.

A number of different triggers can cause asthma symptoms or start an asthma attack:

• infections, usually those caused by a virus (e.g. colds or flu)

• allergens, most commonly from house dust mites, pets or pollen

• exercise, especially in cold weather

• emotions, such as excitement, fear or anger

• irritants, such as air pollution

• smoking people with asthma and the parents of asthmatic children should avoid smoking

• changes in the weather (e.g. a cold spell)

• food additives, such as tartrazine (an artificial food colouring), or food allergens, such as peanuts (sensitized or allergic individuals can have a very severe allergic reaction).

• certain medications some people may be allergic to some drugs (e.g. aspirin).

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