Cats get seasonal allergies to pollen and grass, and some have year-round allergies to fleas and dust mites. Sandy Willis, a veterinary internist who advises the American Veterinary Medical Association, says that when cats interact with an allergen, their body sends immunoglobulin E antibodies to link with it, triggering the release of histamine and other chemicals that cause itchy eyes, runny noses, sneezing, hives and rashes.
The same process happens in other pets (dogs, rats, hamsters) and humans. In rare cases, cats can even be allergic to people. People allergies are uncommon, since we bathe more often than most other species and don't shed as much hair and dead skin—which trigger our own allergies to pets. When cats do have a bad reaction to us, it's usually caused by residue from our perfume, soap or laundry detergent. Any water-based cleaning product usually contains some preservatives. Cats tend to be more sensitive to chemicals than dogs. Specific chemical allergies are difficult to isolate and diagnose, so pets can't be vaccinated for them or build up their tolerance with exposure like they can for organic allergies.
Cats can even be allergic to other pets. Vets offer antihistamines for dogs to treat cat, horse and bird allergies. Cat antihistamines recently hit the market too.
This article originally appeared in the August 2011 issue of Popular Science_ magazine._