Why Do Allergies Cause Asthma?

Allergies and asthma are separate conditions, and allergies don’t actually cause asthma, but people with allergies seem to be more likely to have asthma, and some of the same things (allergens) that cause allergies can also trigger asthma symptoms and asthma attacks. According to the World Allergy Organization, about 50% of adults with asthma also have allergies, and the numbers are higher for children.

What Is Asthma?

Asthma is a disease of the respiratory system (lungs). When people breathe, air is carried into the lungs through the windpipe (trachea), which divides into two tubes called bronchi, leading into each of the sides of the lungs. Inside the lungs, the bronchi divide into smaller and smaller bronchioles, ending up in the alveoli, the air sacs where carbon dioxide leaves the blood to be breathed out and oxygen enters the blood to be taken around the body.

In asthma, a trigger makes the muscles around the bronchioles begin to tighten up, causing the airways to start to close up. The linings of the bronchioles also become inflamed and swell, and produce extra mucus, which makes the airways even smaller. In some people, asthma is triggered by allergens, the things that cause allergy, such as pollen, animal dander, mould spores or dust. This is known as allergic or atopic asthma. Other triggers include cold air, exercise, bacterial or viral infections, cigarette smoke, drugs or chemicals. Stress may make allergic asthma worse.

Symptoms of asthma include coughing, wheezing, chest tightness, shortness of breath and faster breathing. Some people have asthma attacks, where these symptoms get increasingly serious, and they can find it hard to breath. According to Asthma UK, about 5.4 million people in the UK have asthma.

How Is Allergic Asthma Treated?

In people with allergic asthma, avoiding the allergens will help avoid asthma attacks. Some doctors can carry out allergy skin prick tests to work out what the allergens are. If the allergen is pollen, it is a good idea to stay indoors when the pollen count is high. If the allergen is the dust mite, vacuum regularly (including furniture and mattresses) and wash bedding and curtains as often as possible. If the allergen is mould and mould spores, keep the house (especially the bathroom) clean and dry. If the allergen is animal dander fur, saliva and skin), it’s important to keep the animals out of bedrooms, and regular cleaning can keep levels of animal dander low (see ‘Pets for Allergic Children’).

Asthma is usually treated with inhalers, which are described as ‘relievers’ or ‘preventers’. A ‘reliever’ will treat an attack by making the airways wider (bronchodilation), and is used only when needed. In people with mild asthma, this may be enough on its own. A preventer is an anti-inflammatory agent, and if used regularly will help to stop attacks happening. This is usually used in people with more serious asthma, who need to use their reliever inhaler once a week or more.

People with allergic asthma often also have allergic rhinitis (sneezing and runny or blocked nose). Antihistamines will reduce the symptoms of the allergic rhinitis and this can also cut down on asthma attacks. In some people, desensitization therapy (receiving very small doses of the allergen so that the body becomes used to it (see ‘How Do Allergy Drugs Work?’) might help.