What causes asthma, common triggers, treating asthma, diagnosing asthma

What causes asthma?

The cause of asthma is not fully understood, although it is known to run in families. You are more likely to have asthma if one or both of your parents has the condition.

Common triggers

A trigger is anything that irritates the airways and brings on the symptoms of asthma. These differ from person to person and people with asthma may have several triggers.

Common triggers include house dust mites, animal fur, pollen, tobacco smoke, exercise, cold air and chest infections.

Read more about the causes of asthma.

Asthma can also be made worse by certain activities, such as work. For example, some nurses develop asthma symptoms after exposure to latex. This is often referred to as work-related asthma or occupational asthma.  

Treating asthma

While there is no cure for asthma, there are a number of treatments that can help effectively control the condition. Treatment is based on two important goals:

• relieving symptoms 
• preventing future symptoms and attacks from developing

Treatment and prevention involves a combination of medicines, lifestyle advice and identifying and then avoiding potential asthma triggers.

Read more about living with asthma.

Who is affected?

In the UK, 5.4 million people are currently receiving treatment for asthma. That is 1 in every 12 adults and 1 in every 11 children. Asthma in adults is more common in women than men.

Symptoms of asthma

The symptoms of asthma can range from mild to severe. When asthma symptoms get significantly worse, it is known as an asthma attack.

The symptoms of asthma include:

• feeling breathless (you may gasp for breath)
• a tight chest, like a band tightening around it 
• wheezing, which makes a whistling sound when you breathe
• coughing, particularly at night and early morning
• attacks triggered by exercise, exposure to allergens and other triggers

You may experience one or more of these symptoms. Symptoms that are worse during the night or with exercise can mean your asthma is getting worse. Talk to your doctor or asthma nurse about this.

Asthma attack

A severe asthma attack usually develops slowly, taking 6 to 48 hours to become serious. However, for some people, asthma symptoms can get worse quickly.

As well as symptoms getting worse, signs of an asthma attack include:

• you get more wheezy, tight-cheated or breathless
• the reliever inhaler is not helping as much as usual
• there is a drop in your peak expiratory flow (see diagnosing asthma for more information)

If you notice these signs, do not ignore them. Contact your GP or asthma clinic or consult your asthma action plan, if you have one.

Signs of a severe asthma attack include:

• the reliever inhaler, which is usually blue, does not help symptoms at all
• the symptoms of wheezing, coughing, tight chest are severe and constant
• you are too breathless to speak
• your pulse is racing
• you feel agitated or restless
• your lips or fingernails look blue

Causes of asthma

There is no single cause of asthma, but certain things may increase the likelihood of developing it. These include genetics and the environment.

Who is at risk of developing asthma?

Things known to increase the likelihood of developing asthma include:

• a family history of asthma or other related allergic conditions (known as atopic conditions), such as eczema, food allergy or hay fever 
• developing another atopic condition such as a food allergy
• having bronchiolitis as a child (a common lung infection among children) 
• being exposed to tobacco smoke as a child, particularly if your mother smoked during pregnancy 
• being born prematurely (especially if you needed a ventilator) 
• being born with a low birth weight (less than 2kg or 4.5 pounds)

Want to know more?

Asthma triggers

The symptoms of asthma can have a range of triggers, but they do not affect everyone in the same way. Once you know your asthma triggers, you can try to avoid them.

Triggers include:

• Airway and chest infections. Upper respiratory infections, which affect the upper airways, are often caused by cold and flu viruses and are a common trigger of asthma. 
• Allergens. Pollen, dust mites, animal fur or feathers, for example, can trigger asthma.
• Airborne irritants. Cigarette smoke, chemical fumes and atmospheric pollution may trigger asthma.
• Medicines. The class of painkillers called non-steroidal anti-inflammatory drugs (NSAIDs), including aspirin and ibuprofen, can trigger asthma for some people, although are fine for most. Children under 16 years of age should not be given aspirin. 
• Emotional factors. Asthma can be triggered by emotional factors, such as stress or laughing.
• Foods containing sulphites. Sulphites are naturally occurring substances found in some food and drink. They are also sometimes used as a food preservative. Food and drinks high in sulphites include concentrated fruit juice, jam, prawns and many processed or pre-cooked meals. Most people with asthma do not have this trigger, but some may. Certain wines can also trigger asthma in susceptible people.
• Weather conditions. A sudden change in temperature, cold air, windy days, poor air quality and hot, humid days are all known triggers for asthma.
• Indoor conditions. Mould or damp, house dust mites and chemicals in carpets and flooring materials may trigger asthma.
• Exercise. Sometimes, people with asthma find their symptoms are worse when they exercise.
• Food allergies. Although uncommon, some people may have allergies to nuts or other food items, known as an anaphylactic reaction. If so, these can trigger severe asthma attacks.

What happens during an asthma attack?

During an asthma attack:

• the bands of muscles around the airways tighten
• there is increased inflammation in the linings of the airways, which swell
• the airways produce sticky mucus or phlegm, which can further narrow the airways

The passages of the airways narrow, making it more difficult for the air to pass through and, therefore, more difficult to breathe. This can cause the characteristic wheezy noise, although not everyone with asthma will wheeze. In a life-threatening attack, there may not be a wheezy sound.

An asthma attack can happen at any time. However there are usually warning signs for a couple of days before. These include symptoms getting worse, especially during the night, and needing to use the reliever inhaler more and more.

If you or someone else is having a severe asthma attack and cannot breathe, dial 999 immediately for emergency medical treatment.

Diagnosing asthma

If you have typical asthma symptoms, your GP is likely to be able to make a diagnosis. Your GP will want to know when your symptoms happen and how often, and if you have noticed anything that might trigger them.

A number of tests can be carried out to confirm the diagnosis.

Spirometry

A breathing test called spirometry is carried out to assess how well your lungs work. You will be asked to breathe into a machine called a spirometer.

The spirometer takes two measurements: the volume of air you can breathe out in one second (called the forced expiratory volume in one second or FEV1) and the total amount of air you breathe out (called the forced vital capacity or FVC).

You may be asked to breathe out a few times to get a consistent reading.

The readings are compared with normal measurements for your age, which can show if your airways are obstructed.

Sometimes an initial set of measurements is taken, then you are given a medicine to open up your airways (a reliever inhaler) to see if this improves your breathing. Another reading is taken and, if it is much higher after taking the medicine, this can support the diagnosis.

Peak expiratory flow rate test

A small hand-held device known as a peak flow meter can be used to measure how fast you can blow air out of your lungs in one breath. This is your peak expiratory flow rate (PEFR), and the test is usually called a peak flow test.

You may be given a peak flow meter to take home and a diary to record measurements of your peak flow. Your diary may also have a space to record your symptoms. This will help you recognize when your asthma is getting worse.

Other tests

Some people, but not all, may need more tests. The tests may confirm the diagnosis of asthma or help diagnose a different condition. This will help you and your doctor plan your treatment.

Airway responsiveness tests

This test is used to see how your airways react when they come into contact with a trigger. You will be asked to take a mannitol challenge test which involves breathing in increasing amounts of a dry powder. This deliberately triggers asthma symptoms and cause the airways to narrow. In children, exercise is sometimes used as a trigger.

You then blow into the spriometer to measure how much your FEV1 and FVC have changed in response to breathing in the trigger. If there is a significant decrease in these measurements, you may have asthma.

Testing airway inflammation

• Phlegm sample. The doctor may take a sample of phlegm to check whether you have inflammation in the lungs.
• Nitric oxide concentration. As you breathe out, the level of nitric oxide in your breath is measured. A high level of nitric oxide can be a sign of airway      inflammation.

Allergy tests

Skin testing or a blood test can be helpful to confirm whether your asthma is associated with specific allergies, for example to dust mites, pollen or foods.