Plants reproduce by moving tiny grains of pollen from plant to plant. Some pollen is carried by bees. And some is blown by the wind. It’s the wind-blown pollen that causes nasal allergies. The amount of pollen in the air varies from season to season.

House-dust mites are tiny bugs too small to see. They can live in mattresses, blankets, stuffed toys, and carpets. The droppings of these mites are a common indoor cause of nasal allergies.

Mold loves dark, damp areas, both indoors and outdoors. It tends to grow in bathrooms, basements, refrigerators, and in the soil of houseplants. Mold reproduces by sending tiny grains called spores into the air. If these spores are breathed in, they can cause a nasal allergic reaction. Mold is also present in decaying vegetable matter. For example, in piles of wet leaves in a yard.

Pets are common causes of nasal allergies. This includes cats, dogs, birds, horses, and rabbits. Flakes of skin (dander), saliva left on fur when an animal cleans itself, urine in litter boxes and cages, and feathers can all cause nasal allergies. Pests such as rodents can also be a major cause of allergies. This is especially the case in urban settings. They may not even be in your own apartment.

Irritants don’t cause nasal allergies. But they can make allergy symptoms worse. Examples of irritants include:

• Cigarette smoke
• Perfume
• Aerosol sprays
• Smoke from wood stoves or fireplaces
• Air pollution
• Car exhaust
• Strong odors such as from cleaning products