Pet allergy is an allergic reaction to proteins found in an animal's skin cells, saliva and urine. Most often, pet allergies are triggered by exposure to dander (dead flakes of skin) ​a pet sheds.

Generally, pollens that cause allergies are those of anemophilous plants (pollen is dispersed by air currents.) Such plants produce large quantities of lightweight pollen which can be carried for great distances and are easily inhaled, bringing it into contact with the sensitive nasal passages.

Dust mites feed on organic detritus such as flakes of shed human skin and flourish in the stable environment of dwellings. House dust mites are a common cause of asthma and allergic symptoms worldwide.