Allergic rhinitis is caused by an allergic reaction to an allergen. Allergens include pollen, dust, or skin flakes from certain animals.
Common allergens
Breathing in tiny particles of allergens can trigger allergic rhinitis.
Common airborne allergens that cause rhinitis include:
- house dust mites
- pollen and spores
- animal skin and saliva
House dust mites
House dust mites are tiny insects that feed on the dead flakes of human skin. They can live in mattresses, carpets, soft furniture, pillows and beds.
Rhinitis is not caused by the dust mites themselves. But by a chemical found in their poo.
Dust mites are around all year. But their numbers are higher in the winter.
Pollen and spores
Pollen produced by trees and grasses can sometimes cause allergic rhinitis.
Most trees pollinate from late March to May. Grasses usually pollinate from May to September.
Spores produced by mould and fungi can also cause rhinitis.
Animals
Many people are allergic to animals, such as cats and dogs. Animal fur does not cause an allergic reaction. The animal's saliva or skin flakes cause the reaction.
Dogs and cats are the most common animals to cause allergies. But some people are affected by horses, cattle, rabbits and rodents, such as guinea pigs and hamsters.
Being around dogs from an early age can help protect against allergies. There's also some evidence that this might be the case with cats.
Allergens in the workplace
Some people are affected by allergens found in the workplace. These can include wood dust, flour dust or latex.
Oversensitive immune system
The immune system defends your body against infection and illness.
If your immune system is oversensitive, it produces antibodies. Antibodies are proteins in the blood that fight viruses and infections.
Sensitisation to an allergen
The first time you come into contact with an allergen you do not have allergy symptoms.
But your immune system reacts to the allergen as if it is a virus or infection. This starts a process to make antibodies to fight the allergen. The process is called sensitisation.
Re-exposure to an allergen
If you are in contact with an allergen after sensitisation, your immune system:
- Makes antibodies called immunoglobulin E (IgE).
- IgE antibodies cause cells to release chemicals, such as histamine.
- The chemicals can cause the inside layer of your nose to become swollen and make too much mucus.
This can cause the symptoms of sneezing and a blocked or runny nose.
Who is at risk
It's not clear why some people become oversensitive to allergens. But you're more likely to develop an allergy if there's a history of allergies in your family.
The tendency to make too many IgE antibodies in response to harmless substances is called atopy. People who are atopic are more likely to develop allergic conditions.
Environmental factors may also increase the chance of developing allergies, such as:
- growing up in a house where people smoke
- being exposed to dust mites at a young age
