Is the domestic cat allergen Fel d 1 a toxic defence to keep predators away?

by Michael Broad · February 7, 2020

About one in ten people are allergic to domestic cats. This is because of a protein, the allergen Fel d 1, in their saliva which is deposited on their fur, which dries and floats off into the environment as cat dander. It’s a remarkably problematic aspects of our relationship with domestic cats.

Domestic cats and slow lorises have something on common: the protein that makes people allergic to cats.

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Domestic cats and slow lorises have something on common: the protein that makes people allergic to cats. Picture of American SH: Helmi Flick. Slow loris in public domain.

As it happens, the slow loris, a cute looking but venomous primate produces a very similar protein in its armpit glands. When threatened, these fluff monsters put their hands up and lick the glands under their armpits. This allows them to add this protein and other compounds to their spit which is then deposited in the wounds that they make when fighting predators. It causes the wounds to heal very slowly which enhances the prospect of them defending themselves successfully against predators.

This begs the question whether the domestic cat’s allergen exists the same reason. It sounds rather extreme but it is nonetheless an interesting hypothesis. The scientists who carried out a study which is discussed on the sciencealert.com website say that the human’s allergy to cats is so commonplace that it would be a strange coincidence if the allergen hadn’t evolved as a defensive weapon in the way the protein used by slow lorises. Obviously this is speculative and a further study is required.

COMMENT: having giving this some thought, as I must, it seems that the suggestion is unlikely although somewhat compelling because of the very similar nature of the protein produced by these two species. The fact is that the wild cat, the North African Wildcat, which came in out of the wild to domesticate itself with the approval of humans, would not have behaved in this way if it considered the human a predator against which it had to defend itself. That said the physiology of the wildcat has been in place for perhaps hundreds of thousands of years and its origins may have been as a defensive system which subsequently became redundant when the wildcat decided to become a domestic cat.

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Therefore, it seems possible that the cat allergen which so inconveniences many cat owners and prevents many others from adopting a cat despite their love of felines is a redundant defensive system to help fight off predators.

SOME MORE ON FEL D1: