Why Is My Black Cat “Rusting?”

This week, we’re actually answering two questions about black cats, so read on!

Dear Most Esteemed and Knowledgeable Kitties:

I adopted a cat of unknown age from the pound 2 years ago, and over the last 18 months, her fur has gone from very black, to a brown, rusty color. She spends a lot of time sunbathing, plus she gets a holistic cat food, supplemented with fresh fish and meats. I’ve taken her to the vet for her vaccines and checkups and the vet insists she’s in perfect health. I was just wondering what would make her fur change color so dramatically?

~ Ellie

Bella looks “rusty” in bright sunlight. Bella looks “rusty” in bright sunlight.

Thomas: This “rusting” phenomenon is pretty well-known, actually, and the reason behind it has a lot to do with genes.

Bella: You see, there are three variants of the black fur gene. There’s B, the solid black gene; then there’s b, which produces chocolate, and b’, which produces a cinnamon color. The B gene is dominant to the other types.

Thomas: But … the dominant pattern for cat fur is tabby, expressed by the Agouti (or A) gene. In order for a cat to be solid black, a cat must carry the recessive non-agouti (a) gene. Otherwise, a black cat is more or less a tabby in disguise!

Bella: The B gene produces a pigment called eumelanin, which is required to create black fur. But eumelanin is kind of a fragile pigment, especially in black cats with the dominant tabby gene, and heavy exposure to the sun can cause a black cat to turn brownish-red or to have tabby stripes that show in bright sunlight.

Thomas: Another reason why black cats “rust,” which is much rarer, is a deficiency in an enzyme called tyrosine, which is required to produce eumelanin.

Bella: You could ask your vet if it’s possible that a tyrosine deficiency may be the cause of your cat’s rusting, but since you said she spends a lot of time sun bathing, there’s a 99% chance that her fading black is because of sun exposure.

Our friend Abby has a white spot, and she’s special too!

Dear Most Esteemed and Knowledgeable Kitties:

A long time ago I was told that if a black cat had no white anywhere, there was something special about that. What was the special about? I have a stray black kitten, four months old who I’ve taken in and has no white.

~ Trisha

Bella: Speaking as a black cat, I’d have to say that all black cats are special, including those with white spots.

Thomas: The special thing about cats with no white spots has a lot to do with genetics, too. There’s a dominant gene for spotting (S) that produces spots of white that mask your cat’s real color. This produces tuxedo cats, “cow kitties,” and cats with white boots and mittens like me!

Bella: A black cat with the recessive s (non-spotted) gene will have no white spots.

Thomas: But another thing that makes solid black cats special is that in many countries they’re considered good luck!

Bella: And rightly so: It’s been known for quite some time that black fur confers health advantages to cats because the gene for black fur apparently also brings increased resistance to disease.

Thomas: Wow! No wonder Siouxsie was healthy for so long!

Bella: I hope I live to be really old, too.

Thomas: So, do you have any other questions about black cats? Why do you think black cats are special, and do you have a rusty black cat? Let’s talk in the comments!