Allergic reactions to domestic cats are common—more common than dog allergies, for example. People can, after a first exposure, become allergic to almost anything; the allergy is simply the response of the immune system to a stimulus it perceives as threatening. Almost all animals will cause allergies in a percentage of the people who habitually handle them. For example, I’ve known of laboratory workers who developed allergies to grasshoppers and armadillos. This is simply a flaw in the human immune system. In the case of cats and other mammals, it’s usually the dander that provokes the reaction—the dead cells of the epidermis, which all of us mammals continually and involuntarily slough.
A hint about the nature of cat allergies comes from an unexpected direction. Scientists studying a lemur-like primate called the slow loris found that it defends itself from predators with a venomous bite. The venom is secreted by glands on the loris’s arms, then licked onto the teeth. Mother slow lorises rub this venom onto the coats of their young. When the mother is away from the nest, the poison protects the young from predators. Scientists have analyzed this venom and found its active components chemically similar to the allergenic components in cat dander. This finding suggests cat dander is a defense mechanism, a deterrent. Predators with more sensitive noses than ours might be repelled by the dander, or might have been at some earlier stage, before the attackers or the cats themselves evolved away from this dynamic. Perhaps this has something to do with the cat’s habit of raising its hackles when it feels threatened—a method of flinging noxious dander. In any event, these speculations, if they prove true, help to explain why cats are disproportionately represented among the sources of allergy.