Allergy is caused by normally harmless substances in the environment (allergens). Common allergens include house dust mite and pet dander. Other possible allergens include moulds, grass or pollen.
House dust mite
House dust mites are microscopic creatures that thrive on skin flakes shed by humans. House dust mite droppings that are inhaled and can trigger Allergic Rhinitis. It can be difficult to avoid house dust mites, but dust mite resistant bedding, washing bedding in hot water (60 ºC), and minimising dust collecting fabrics like carpets or curtains may help reduce exposure.
Pet dander
A cat or dog kept in the house soon becomes part of the family and is very difficult to exclude after that point, but their sheddings can sometimes be a trigger for allergies. It has been documented that it takes six months of normal, routine house cleaning to rid a house of pet dander after the pet has left the house.