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NHS Choices - Causes of allergic rhinitis

(19/05/2014)

Allergic rhinitis is caused by an allergic reaction to an allergen, such as pollen, dust and certain animals.

Oversensitive immune system

In cases of allergic rhinitis, the immune system (the body's natural defence against infection and illness) reacts to an allergen as if it were harmful.

If your immune system is oversensitive, it will react to allergens by producing antibodies to fight them off. Antibodies are special proteins in the blood that are usually produced to fight viruses and infections.

Allergic reactions do not occur the first time you come into contact with an allergen. The immune system has to recognise and 'memorise' it before producing antibodies to fight it. This process is known as sensitisation.

After you develop sensitivity to an allergen, whenever it comes into contact with the inside of your nose and throat, it will be detected by antibodies called immunoglobulin E (IgE).

These cause cells to release a number of chemicals, including histamine, which can lead to swelling of the mucus membrane (the inside layer of your nose) and the production of excess mucus. This is what causes the typical symptoms of sneezing and a blocked or runny nose.

Common allergens

Allergic rhinitis is triggered by breathing in tiny particles of allergens. The most common airborne allergens that cause rhinitis are described below.

House dust mites

House dust mites are tiny insects that feed on the dead flakes of human skin. They can be found in mattresses, carpets, soft furniture, pillows and beds.

Rhinitis is not caused by the dust mites themselves, but by a chemical found in their excrement. Dust mites are present all year round, although their numbers tend to peak during the winter.

Pollen and spores

Tiny particles of pollen produced by trees and grasses can sometimes cause allergic rhinitis. Most trees pollinate between early to mid-spring, whereas grasses pollinate at the end of spring and beginning of summer.

Rhinitis can also be caused by spores produced by mould and fungi.

Animals

Many people are allergic to animals, such as cats and dogs.

It is not animal fur that causes the allergic reaction, rather flakes of dead animal skin and their urine and saliva.

Dogs and cats are the most common culprits, although some people are affected by horses, cattle, rabbits and rodents, such as guinea pigs and hamsters.

Work-related allergens

Some people are affected by allergens found in their work environment, such as wood dust, flour dust or latex.

Who's most at risk?

It is not fully understood why some people become oversensitive to allergens, although you are more likely to develop an allergy if there is a history of allergies in your family.

If this is the case, you are said to be 'atopic' or to have 'atopy'. People who are atopic are more likely to develop allergies because they produce more IgE antibodies than other people.

Environmental factors also seem to play a part. Studies have shown certain things may increase the chance of a child developing allergies, such as growing up in a house where people smoke and being exposed to dust mites or pets at a young age.