According to Allergic Pet, dogs are susceptible to cat allergies, which are caused by the allergen FelD1, a protein found in cat saliva. Cats are fastidious groomers, and the allergen sticks to their coats, dries and drops from the fur.
FelD1 is nearly weightless, and it tenaciously sticks to walls, furnishings, carpets and drapes. It is very persistent and often stays active in a home for up to 10 years. Similar to humans, a dog develops allergies when his immune system mistakenly interprets a common, harmless allergen as dangerous, leading to an extreme reaction. Airborne allergens are effectively controlled by HEPA air filters.