What causes hayfever?

Several factors can trigger hayfever symptoms or make them worse. Knowing your triggers can help you limit exposure and manage your condition.

Hayfever is an allergic reaction to substances in the air, like tiny particles of dust, or plant matter. For some people, exposure to these substances, called allergens, can trigger the immune system to overreact and lead to hayfever symptoms.¹

Common hayfever triggers in Australia

The airborne particles that trigger hayfever are usually too small to be seen, so it can be difficult to know if they are in the air. However, there are some common triggers to look out for:

Pollen

Grass, tree and weed pollen are common environmental triggers. Pollen allergies usually occur in spring and summer, although the timing and severity of pollen season varies considerably between years and places.^1,2

Pets

Pets shed saliva and dead skin, known as pet dander, and both of these can cause allergies. Pet dander, like pollen, can cling to clothing, furniture and even walls, so you may experience symptoms just by being near a pet owner.^1,3

Moulds

They are a type of fungus that thrive in warm, damp conditions, such as in bathrooms, under sinks and in wardrobes. Moulds can release spores into the air, which may cause an allergic reaction when inhaled.^1,4

Dust mites

These are microscopic insect-like pests that live in fabric. Household items such as bedding, carpet and children’s soft toys provide an ideal environment for dust mites.^1,5

Hayfever causes an immune response

Your immune system is your body’s first line of defense against hayfever triggers, although not everyone will respond to the same trigger or in the same way. For instance, if you have a pollen allergy, your immune system treats pollen as an allergen and tries to get rid of it.⁶

When you breathe in an allergen, your immune system responds by producing antibodies called Immunoglobulin E (IgE). These antibodies bind themselves to the allergen and travel to a type of immune cell called a mast cell, causing a release of histamine and other chemicals. The release of these chemicals drives inflammation, which leads to hayfever symptoms.^6,7

Hayfever treatments are available. Learn more.

Why do I have hayfever?

Hayfever affects nearly 1 in 5 Australians every year.⁸ It is unclear why some people react to hayfever triggers and others do not, but certain factors may increase your risk of developing hayfever.

Family historyGenetics play a role in allergy, including hayfever. Your risk of hayfever increases if one or both of your parents have it.⁹
Exposure to pollutantsCigarette smoke and car exhaust fumes can cause irritation in the nose and throat and make you more sensitive to hayfever.⁹
Health conditionsHaving asthma or another allergic condition can increase your chance of having hayfever.⁹
Migration effectCertain intercontinental immigrants may develop hayfever after living in a new place for some time.¹⁰