The most common allergens that trigger symptoms are airborne particles which are breathed in to the nasal passages and lungs.

Pollen €“ tree, grass or weed allergy commonly known as hay fever.

House Dust Mites €“ these insects feed on human dead skin and can be found in mattresses, beds, pillows, carpets and soft furnishings. The allergic reaction is caused by a chemical in the mites' faeces, which is very fine, easily breaks up and becomes airborne and is then inhaled, the reaction is not from the mite itself.

Pets €“ most people believe that pet fur or feathers cause an allergic reaction but it is actually the animals' flakes of dead skin, urine and saliva. The most common sources are cats and dogs, but some people are affected by rabbits, guinea pigs and birds. Infestations of mice and cockroaches can also trigger allergic reactions.

Fungal Moulds and Spores €“ fungal moulds can grow anywhere in a house but like natural materials and warm damp places such as bathrooms and kitchens. It is not the fungus that causes the reaction but the tiny spores that are released and inhaled.

Occupational Allergies €“ there are a number of allergens that can be found in workplaces that can trigger reactions such as chemicals, wood dust, latex, animals and flour dust.