With rabbits, rats, mice, hamsters and guinea pigs the most important sources of allergens are the saliva and urine. Once dry, these secretions become airborne and can be a source of allergic reactions for children and laboratory animal workers. Horse and cow skin scales can be allergenic to those exposed to them. Birds carry allergy-provoking mites, molds and pollen on their feathers. Budgie droppings can release proteins into the air which induce insidious lung problems and asthma.
Tropical fish may be problematic, in that individuals can develop allergies to the ant's eggs upon with the fish feed, and mold that may grow in the fish tank. Even cockroaches, although not considered pets, are also a source of domestic allergens.