Consistent, sustained exposure to birds causes bird allergies. Individuals at risk include those who own birds as pets, or who work with birds on a daily basis. The major sources of allergens that cause people to react include:

• Feather dander. Known as “feather dust,” this occurs when feather shafts disintegrate slowly into a powdery dust, or dander. Some birds create so much dander that they coat most surfaces in a room nearly every day. They are referred to as powder-down birds, and include cockatoos, cockatiels and African grey parrots. The dust produced by powder-down birds is sucked into furnace air filters and duct work and distributed everywhere in the house.
  
  
• Bird feces. Often a source of bacteria, dust, fungi and mold. These allergens can become airborne when bird feces dry and trigger symptoms.

Dirty bird cages, overcrowded cages and the excessive amounts of feather dust shed by certain types of birds are some of the factors that create the levels of allergens likely to trigger a reaction. Larger parrots are among birds known to produce great amounts of feather dust.

Feather dust is also found in products that use bird feathers, such as pillows, comforters and down jackets. In some people with bird allergies, use of these products can lead to an allergic reaction.