Get

In Your Inbox

Catster is reader-supported. When you buy via links on our site, we may earn an affiliate commission at no cost to you. Learn more.

What Is Cat “Rust”? Causes & What to Look Out For (Vet-Verified Info)

Black cats have long been associated with bad luck, but their luck has changed significantly in the last few decades. With the rise of social media cat groups, more and more people come together to discuss their love of “voids”, so named for their dark coloration and tendency to look like a cat-shaped void in pictures.

No matter how dark your black cat is, you have likely seen your cat napping in a nice sunbeam and noticed a reddish brown coloration on your cat. Is your cat becoming bleached or changing colors with age? If you’ve noticed this color shift in your black cat, then you’ve seen cat “rust”. It’s relatively common for black cats to develop “rusting”, but you may only be able to spot it when your cat is in direct sunlight. Come with us as we discuss this interesting phenomenon!

divider cat faces oct 2024

What Is Cat Rust?

Cat rust is given this name because of its tendency to appear as a rust brown color, making it look like your seemingly black cat has rusted.

In some instances, you may not be seeing rust. If your cat’s coat is a lighter shade of black or more of a dark grey, then it’s possible that your cat has a pattern to their coat that is not immediately evident but that becomes visible in certain lighting.

Black cat outside of house
Image By: Zemiko, Shutterstock

What Causes Cat Rust?

There are two main causes of cat rust.

Sun Exposure

The pigment that is required to produce black fur is known as eumelanin. This pigment is considered somewhat fragile, and this fragility means that the loss of the pigment often results in the coat turning to a rust color. This risk is much higher in cats that frequently spend time in the sun. Excessive exposure to the sunlight isn’t going to result in your cat’s coat rusting. It’s also associated with certain cancers in cats, such as squamous cell carcinoma.

Tyrosine Deficiency

A less common cause of rusting in cats is a tyrosine deficiency. Tyrosine is crucial for the production of eumelanin, the pigment responsible for black fur. Cats can produce tyrosine by converting phenylalanine, an essential amino acid obtained through their diet. However, if their diet is deficient in both tyrosine and phenylalanine, eumelanin production may decrease, causing black fur to take on a reddish-brown hue. Tyrosine and phenylalanine requirements can vary among individual cats, therefore, if you notice this change, it is important to consult a veterinarian to evaluate your cat’s diet and make any necessary adjustments. It is not recommended to give your cat any tyrosine supplements without your vet’s supervision.

Signs of Tyrosine Deficiency In Cats
  • Rusting of black fur
  • An abnormal, uncoordinated gait
  • Tail bending forward
  • Ptyalism (excessive saliva production)
  • Vocalizing excessively
  • Hyperactivity
  • Weight loss (in kittens)

Though a change in fur color might be perceived as non-threatening, it’s fairly obvious that the other signs of a tyrosine or phenylalanine deficiency are considerably serious. Therefore, your cat should be looked over by a veterinarian if you see any of the signs mentioned above.

If you need to speak with a vet but can't get to one, head over to PangoVet. It's an online service where you can talk to a vet online and get the advice you need for your pet — all at an affordable price!

PangoVet_Mention-in-Content for PangoVet2 save money

divider cat faces oct 2024

Conclusion

It’s somewhat common for black cats to develop rusting of their black coat. Cats tend to spend a lot of time in the sun, often napping in sunbeams throughout the day. If your cat is turning rusty, it’s usually attributed to excessive sun exposure or a nutritional deficiency.

If your cat is developing noticeable rusting of their coat in conjunction with notable signs of a medical condition, like an abnormal gait, hyperactivity, and weight loss, then your cat needs to be seen by a vet to get them diagnosed and treated quickly.


Featured Image Credit: Gavin Allanwood, Unsplash

How useful was this post?

Click on a star to rate (you can leave written feedback after clicking submit)

Help us improve Catster for pet parents!

Your feedback really matters.

What did you like about this post? Also how can we improve it?

Join the conversation

Leave a Reply

You’re very welcome to leave a comment or question. Please know that all comments must meet our community guidelines, and your email address will NOT be published. Let’s have a positive and constructive conversation.

Talk With A Vet Online

Peace of mind,
anywhere, anytime

Affordable vet advice

100+ Pokémon Inspired Cat Names: Ideas for Unique & Adorable Cats

We understand how explosive the cultural phenomenon Pokémon has become and how passionate their fan base is…because we happen to be a part...

15 Amazing Comic Book Cats (With Pictures)

Comics display incredible feats of artistry, storytelling, and imagination. Some are funny, others provide cutting social commentary, and there are also superhero comics...

Ragamuffin Cat vs Maine Coon: Main Differences (With Pictures)

When shopping for a new pet to enter their lives, people usually narrow it down to two different breeds. If you have your...

Should I Let My Cat Sleep With Me? Vet-Reviewed Pros & Cons

Having cats sleep on their owners’ beds is an ongoing debate. There are some benefits to having your bed sleep on your bed...

More related

How to Stop a Cat From Licking Everything: Our Vet Discusses Reasons, Remedies & FAQ

You know that cats groom themselves, so you’re not surprised to see your kitty licking until you realize they’re constantly licking things. Is...

Why Does My Cat Reach His Paw Out to Me? 9 Vet-Verified Reasons

There are several reasons that your cat may reach out to you, whether they are lying down or lightly tapping you with their...

9 Best Outdoor Automatic Cat Feeders in 2025 – Reviews & Top Picks

If your cat loves to spend time outside while you’re at work, you might be wondering how to keep them well-fed during the...

Catster Photo Contest: Cats of the Week Winners (July 24, 2025)

Every week our team gets the privilege of sorting through our readers photos to choose what cats will win this weeks contest! See...

Keep reading

Can Cats Eat Animal Crackers? Vet Reviewed Facts

Picture the scene: You’ve stolen a few minutes to enjoy some animal crackers, and your cat comes over, settles at your feet, and gives you the “eyes” or a swipe at your hand if you’ve got a feisty feline. We...

Can Cats Eat Animal Crackers

10 Best Pellet & Pine Cat Litters in 2025 – Reviews & Top Picks

Being a cat owner can be one of the most rewarding experiences for us humans, but one of the distinct disadvantages is dealing with the litter box. Part of the unpleasantness of litter boxes is the rather pungent odor of...

wood-pellet-cat-litter

Do Cats Eat Snakes? Vet-Verified Risks & Precautions

Cats are opportunistic hunters and sometimes hunt snakes as a result. Cats often hunt snakes for sport and leave the body after the game. Occasionally, cats will eat snakes, but it doesn’t happen frequently enough that you should rely on...

cat staring at snake

How to Stop a Male Cat From Mounting: 7 Vet-Reviewed Reasons & What To Do

Watching your male cat mount various objects, you, or even other animals around your home can be frustrating and confusing. It doesn’t make sense, especially if your cat is neutered. To get the behavior to stop, we have to understand...

cat humping another cat

Can Cat Pee Make You Sick? Vet-Verified Facts & Safety Tips

We all know that cat pee smells awful, but did you know that cat pee can be harmful to you and can cause allergic reactions in people who are allergic to cats? But just how dangerous is cat pee, can...

cat-peeing-on-the-bed

Cats Peeing on Shoes: 7 Vet Reviewed Reasons & How to Stop It

Nothing is worse than slipping your feet into a pool of cat pee—in your own shoe. If your cat has made a habit out of weeing into your Nikes, you’re looking for solutions. But before you can stop the problem,...

tabby-cat-pees-on-shoes

Cat Hairballs: Our Vet Explains How to Treat Them

Yuck! Your cat had retched up something long and hairy. Is it a mouse that didn’t get digested? Chances are that your cat has just vomited up a hairball. Let’s look at what causes hairballs and how you can try...

cat choking or gagging

Inhaler for Cats: Vet-Approved Tips on How to Use It for an Asthmatic Feline

Feline asthma is a respiratory condition that results from inflammation and muscle constriction in the airways. It is not well-understood in cats, but is often treated similarly as asthma in humans. There are several treatments for asthma in cats, including...

Treating a cat for asthma with an inhaler