How are allergies and asthma related?

Approximately 70-80% of asthma in New Zealand is associated with allergy. Sometimes more than one part of the body can be affected by allergens, which is why many people with asthma also experience hayfever and eczema.

What is an allergy?

An allergy occurs when the body's immune system over-reacts to normally harmless substances (called allergens). These substances may be in the air, water or in things you touch or eat.

What happens?

When an allergic person comes in contact with an allergen, their immune system produces a special kind of antibody (IgE). The antibody triggers the release of histamine and other chemicals within the body that cause the allergy symptoms. Also see: Allergic rhinitis and hayfever

What are the most common allergens for people with asthma?

In New Zealand, the most common asthma-producing allergens are related to house dust mites, animals, pollens, moulds and fungal spores. Asthma due to food and drink allergy is uncommon.

What can I do to reduce the risk of allergy-associated asthma?

If you have asthma which is triggered by allergens you should try to identify the allergen, in order to avoid or minimise exposure to it.

There is little evidence that avoiding allergens in childhood will prevent the development of allergies. In fact, exposure to animals may reduce a child's risk of allergic disease; however, more research is needed in this area.  Once allergic asthma has developed, however, it is important to minimise exposure to avoid triggering asthma attacks.

How can I find out what I am allergic to?

Skin prick test: A skin prick test can help to determine if a substance is a trigger. This involves testing a small amount of the suspected allergen on the skin to see if a reaction occurs. A positive reaction is when an itchy red swelling with a weal (wheal) develops in 15-20 minutes (looks a little like chicken pox). This subsides within a couple of hours.

A positive reaction does not always mean the substance reacts in the same way in the lungs. Other information, such as clinical symptoms, needs to be taken into account to determine if the substance is an asthma trigger.

Note that skin prick tests are generally not used for children under the age of three, as they are less reliable in young children.

Specific IgE or RAST: The radioallergosorbent test (RAST) measures the amount of IgE in the blood that is directed to a specific allergen. It identifies reactions to specific allergens, eg, dust mite, pollen, animal dander, moulds, foods and some insect venoms. A positive response does not necessarily mean that the allergen tested is a major trigger.

If you are interested in having one of these tests, or would like more information about them, you should discuss this with your doctor.

Related topics

Also see: Understanding Allergy and Asthma triggers 

Original material provided by The Asthma Foundation of New Zealand, 2010. Reviewed by everybody, December 2010.