Chances are, you know at least one person with a cat or dog allergy; roughly 10–20 percent of people worldwide exhibit some form of allergic symptoms to these common household pets. Given how common allergies to other species are, you may wonder: Can the opposite be true? Could a cat or dog have an allergic reaction to their owner, or to humans in general?
Maybe, says Douglas Deboer, a dermatologist at the School of Veterinary Medicine at the University of Wisconsin-Madison. There has been some research and experiments that suggest the possibility that pets can be allergic to humans, but nothing conclusive. If there are cats or dogs with these allergies, they are extremely rare.
“Anything’s possible,” Deboer says. “But it seems clear that it is not very common, if it exists at all.”
Deboer, whose research focuses on skin diseases and allergic reactions in household animals, says reactions to dogs or cats typically occur when someone is allergic to the animal’s dander, flakes of dead skin cells shed from the body. So, in the event that pets can have allergic reactions to human beings, those reactions would stem from exposure to human dander. Deboer says there have been allergy tests done on household pets, but most of these test results are negative. A very small amount of tests, roughly less than 2 percent, show a reaction to human dander.
However, Deboer says that’s far from a conclusive result. Allergy tests aren’t perfect, and have a fairly high rate of false positives. Humans who have grappled with food allergies and elimination diets might be able to predict the next step: To confirm that a household pet is actually allergic to humans, you would need to isolate them from people and find demonstrable evidence that their conditions improve. Then, the pet would need to be brought back to an environment with humans to confirm it made their condition worse. Given the difficulty of performing a test where cats would be completely isolated from humans for a significant length of time, there haven’t been any conclusive studies that have proven a human-induced allergy in a cat.
Elia Tait Wojno, an immunologist at the University of Washington, says that allergy testing for dogs and other pets is quite rare, which is part of the reason why it's unclear if these animals can be allergic to humans. Generally speaking, even when a dog is demonstrating clear signs of atopic dermatitis or skin allergies, veterinarians will often prescribe them allergy management medication rather than running a full allergy test to determine the root cause. So, it becomes difficult to understand, on a population level, how many dogs have allergies and what they are actually allergic to.
That said, although the existence of human allergies in cats and dogs is up for debate, there is evidence to suggest that household pets can be allergic to one another. Although it’s not common, there have been cases where cats, who are more prone to develop allergic asthma symptoms, have shown allergies to dogs.
Tait Wojno says that, like human allergies in pets, it’s an area where scientists have relatively little understanding. She hopes further research will reveal more about how allergies manifest in household animals. “I think that's an area of ongoing research that will be important as we learn how to treat these allergies better,” Tait Wojno says.