Six Common Indoor Airborne Allergens

1. Pollen

Pollen allergy is an allergic condition caused by inhaling airborne pollen antigens. There are usually two peak seasons each year: spring and summer to autumn. Spring pollen commonly comes from trees such as elm, poplar, willow, pine, cypress, and birch, while summer and autumn pollen often comes from weeds and crops. Pollen grains are microscopic, light, and abundant, so contact and inhalation can readily trigger sensitization.

2. Fungi

Fungi mainly occur in soil and decaying organic matter. Both fungal hyphae and spores can be allergenic, with spores generally posing the greater risk because wind can disperse them widely. Common groups include Cladosporium, Alternaria, Penicillium, Aspergillus, and yeasts. Poorly maintained ventilation systems and soil in indoor flowerpots can also support fungal growth.

3. Dust mites

Dust mites are microscopic arachnids found throughout the home, especially in dust from mattresses, sheets, pillowcases, upholstered furniture, plush blankets, and soft toys. They feed on shed human skin. Living and dead mites, body fragments, eggs, secretions, droppings, and cast skins can all act as allergens.

4. Animal dander

A susceptible person can become sensitized after prolonged contact with an animal. Once sensitized, even a small amount of dander may trigger nasal symptoms. Common sources include pets such as cats and dogs and livestock such as cattle, horses, and sheep.

5. Feathers

Feathers from poultry, bedding, pillows, clothing, and pet birds can act as allergens.

6. Household dust

Household dust is a common trigger of perennial rhinitis. Its composition is complex and can include animal, plant, and chemical materials, as well as decaying matter, fibers and debris from bedding, clothing and old furniture, skin flakes, bacteria, and fungi. Dust composition varies substantially by source, so individual allergic responses may also differ.