A number of indoor mammals, birds and crustaceans can produce proteins which can cause allergies and worsen asthma in sensitive people. Dust mites, cockroaches, birds, mice, rats, cats, dogs, horses, pigs and cattle all produce allergens in their droppings, salvia, skin, fur or feathers. Exposure to these allergens have been linked to higher skin test reactivity and higher rates of asthma and wheezing.
A review of 9 US studies reported that many household factors are associated with animal allergens. Presence of mold or water damage, cracks and holes in walls, and presence of food on floors and carpets were associated with higher levels of allergens from mites, cockroaches, rats and mice. Use of less toxic pesticides like boric acid can reduce cockroach numbers.
Keeping dogs or cats were associated with higher levels of allergens from these animals. Bathing cats can significantly reduce indoor cat allergen levels, but many cats do not like to bathe. Some studies have reported, however, that significant levels of cat and dog allergens can be present in homes without a cat or dog. Significant levels of cat and dog allergens can enter the home through occupants clothes. (On the other hand, pet dogs and cats provide companionship and reduce stress. Some studies have reported that having a cat or dog can reduce risk of depression and heart problems.) To reduce bird allergen exposure indoors, be sure to clean bird droppings and feathers promptly.
Some interesting research on indoor allergen levels was published by Wilson et al. in the February 2010 Environmental Research.
The most common animal allergy indoors involves allergy to dust mites. Dust mites live on dead skin, hair and feathers. They require a humid environment to grow. Indoor dust mite allergen levels may be significantly decreased by the encasing bedding in mite resistance pillowcases and sheets, and by using air conditioners and dehumidifers to reduce humidity.
I have written an article on dust mite allergens in the June 1996 journal Allergy. For a free copy of this article- please contact me at LukeTCurtis@aol.com