Stupid Question ™
June 15, 2000
By John Ruch
Q: Are cats and dogs ever allergic to humans the way humans are to cats and dogs?
—Lucas A. Gualtieri
A: The purely logical answer is, “Yes.”
But science, with its niggling demands for experimental proof, says, “Maybe, and if so, we don’t know how allergic.”
Here’s what we do know.
About the same percentage of humans and pets suffer from allergies of some kind: 10 to 20 percent of the population.
Cats and dogs have the same sort of allergies humans have (pollens, molds, dust, insect bites, food), to the degree that human allergists are sometimes consulted by vets for local pollen information.
The biology is also nearly identical—the big exception being that cats and dogs have most of their histamine receptors (the cells that result in allergic inflammation) in their skin, whereas humans have a lot in the respiratory tract. So pet allergies usually take the form of skin disease.
Allergy tests and treatments are also nearly identical in humans and pets. Your dog may even take Benadryl.
When a human is allergic to cats or dogs, the allergen (the offending substance) is a protein in the animal’s skin, saliva and/or urine. Skin flakes, or “dander,” containing the protein float around and become a big problem.
Human skin also flakes off, at a rate of around one-fifth of an ounce a week. It certainly contains proteins. In fact, it’s not unheard of for humans to be allergic to another human’s proteins.
“You could literally be allergic to semen,” said Anthony Szema, directory of the Allergy and Asthma Center of the State University of New York at Stony Brook. “There’s literature on that.”
So, as Ohio State University (OSU) veterinary dermatologist Andrew Hillier said, “it seems very likely” that some animals are allergic to human dander. Indeed, OSU Small Animals Medicine Professor Kenneth Kwochka said that tests have shown some cats and dogs have skin reactions to human dander.
Textbooks cite US and European studies showing anywhere from 17 to 67.8 of allergy-suffering dogs reacting to human dander in allergy tests. Dogs have also been known to react to the dander of cats and other dogs. (All this talk is about dogs because they tend to suffer from allergies more than cats do.)
However, an allergy test doesn’t necessarily mean anything. Allergy-prone dogs are usually allergic to several different things, and test doses are unnaturally high. A positive reaction doesn’t automatically mean the animal is actually allergic, or if it is, whether it’s allergic enough to suffer symptoms in real life.
Testing itself is difficult. According to Hillier, allergy test kits in the US don’t contain human tissue because it might be infected with diseases. So widespread testing simply isn’t being done.
Current conventional wisdom is that some pets probably are allergic to their owners—but that it’s far from common.
Information in this field is likely to improve, just as it did on human allergies. Szema points out that it’s only been 10 years since the genetics of allergies were discovered—and only 100 years since human allergies to dogs and cats were confirmed as real.