What is asthma?

What is asthma?

Asthma affects the small airways (bronchioles) that carry air in and out of the lungs. If you have asthma your airways can become inflamed, swollen and constricted (or narrowed) and excess mucus is produced.

More than 5.2 million people in the UK are being treated for asthma and about 1.1 million of these are children. Asthma affects approximately one in 12 adults and one in eight children in the UK. This means there is a person with asthma in one in five households in the UK. It can affect almost anyone, at any age, anywhere although it tends to be worse in children and young adults.

Asthma is becoming increasingly common in the developed world and is now the most common chronic condition in the west. Aspects of the modern environment that are thought to be contributing factors include:

• Air pollution
• Processed foods
• Centrally heated and double-glazed houses (ideal breeding grounds for house dust mites)

Asthma symptoms

An asthma attack describes the symptoms of tightness in the chest, a wheezing or whistling noise in the chest, coughing and difficulty breathing that occur when the airways become narrowed, inflamed and blocked by plugs of mucus.

An attack can occur suddenly. However, many people with asthma learn to recognise the warning symptoms - such as an itchy nose or itchy skin, dizziness or light-headedness, or an irritating cough.

Learning the warning signs can often alert someone with asthma in time to take preventive action.

Asthma is a chronic condition, which means attacks occur over a long period of time. Although there are times when acute episodes strike asthmatics, most people can say there are long periods during which they have few, if any, symptoms.

The main symptoms of asthma are:

• Coughing
• Wheezing
• Shortness of breath
• Tight feeling in the chest

Causes of asthma

Asthma has many different causes, but scientists still don't know exactly what these are. You may have oversensitive airways, a family history of asthma or be allergic to one or more asthma triggers.

Some doctors believe the airways become oversensitive because cells in the lungs are damaged by viruses. Others believe the initial damage is caused by an allergic reaction causing the lungs to overreact to viral infections.

One of the most common predisposing factors for asthma is an allergy to:

• House dust mites
• Mould spores
• Pollen
• Pets
• Food allergies

Most people find there are several things that can trigger their asthma.

Genetics and asthma

Asthma tends to run in families that are prone to allergies. So, belonging to a family where some members have asthma and others have other allergies, such as eczema, hay fever or allergic rhinitis, makes a person more likely to have asthma themselves.

However, because there are so many factors involved, it can be difficult to predict exactly who in a family will develop the condition.

Although asthmatic and allergic tendencies are inherited, there is no single gene involved. Rather, there are a number of different ones that react with factors in your environment to trigger the onset of asthma.

Scientists are searching for the genes involved in asthma that may eventually lead to a cure.

Environmental factors and asthma

Environmental factors that increase the risk of developing asthma include:

• Exposure to allergens during pregnancy (for example from foods in the mother's diet) that sensitise the unborn baby's immune system
• Infections such as colds during early life
• Being brought up in a house where there is a pet (especially a cat)
• Being introduced to certain foods such as cow's milk and eggs at a young age
• Being born at a time of year when the pollen count is high
• Being exposed to cigarette smoke in the uterus or early life - babies whose mothers smoke are twice as likely to develop asthma
• Air pollution

Thanks to Royal Brompton & Harefield NHS Trust for allowing BBC Health to take photos.