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)

Share

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

Want content like this delivered to you?

Sign Up For Our Newsletter

News, insights, expert advice, and everything cat

* By submitting, you agree to our Terms & Conditions and Privacy & Cookies Policy.




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

One in 100 Cats Gets Diabetes – Here’s How to Catch It Early

One in every 100 cats develops diabetes.1 That’s not a rare, unlucky condition reserved for cats with obvious health problems. It’s common enough...

Dramatic Rescue Turns Into Dramatic Reunion

What started as a routine call for the RSPCA became a heroic, five-hour rescue featuring one trapped and traumatized cat, an emotional family...

Ask Dr. Paola – Help! How Do I Know if it’s Ear Mites! (May 4, 2026)

Welcome to our “Ask Dr. Paola” series, where every Monday we bring expert advice straight from Dr. Paola Cuevas (MVZ) to help our...

Hope for the Tiniest Fighters: Baby Kitten Rescue | Heroes of the Pet World

In a world where the smallest and most vulnerable animals are often the easiest to overlook, Caroline and Baby Kitten Rescue’s work is...

More related

How Much Attention Does a Cat Need? Vet-Reviewed Facts

While cats are often perceived as independent pets, they still require daily attention from their owners. Most cats need at least 20-30 minutes...

Can Cats Eat Vaseline? Vet-Approved Benefits & Precautions

Vaseline is a staple item in many people’s bathroom cupboards. It’s useful for many things, but have you ever considered using it on...

Can Cats Overdose on Catnip? Our Vet Answers

There is nothing quite like the amazing reaction many cats have with catnip. While individual cats’ responses to it can vary greatly, most...

Why Does My Cat Lick Windows & Window Screens? Behaviour Explained

Cats exhibit all sorts of strange and wacky behavior. For instance, you may find some cats licking windows or window screens. Sometimes, cats...

Keep reading

How to Get Rid of Cat Dandruff: 6 Vet-Approved Tips and Tricks

Dandruff is common in cats and is generally a sign that your pet has dry skin. But the causes of dry skin can vary from a simple lack of sufficient humidity in the air to more serious conditions such as...

cat fur with dandruff

WholeHearted Cat Food Review in 2026: Recalls, Pros & Cons

Review Summary WholeHearted pet foods was created by Petco in 2016, beginning with a line of affordable dog food, and cat foods were introduced a year later. Petco is a pet food and pet accessory company founded in the 1960s...

Wholehearted Cat Food Review

Can Cats Eat Lollipops? Health Risks & Vet-Approved Alternatives

Cats are curious creatures, and they often want to try things we eat, so it’s not unusual to wonder if cats can eat lollipops. The answer is, unfortunately, no. Lollipops are made with sugar and other ingredients that can be...

Can Cats Eat Lollipops

Can Cats Eat Cream Cheese? Vet-Reviewed Nutrition Facts & FAQ

Most cats love dairy foods. The stereotypical cat loves milk, though it may upset most actual cats’ stomachs. But what about cream cheese? While cream cheese isn’t toxic to cats, it isn’t exactly the best option for them either. Cream...

Can Cats Eat Cream Cheese

10 Best Cat Foods for Senior Cats in 2026 – Reviews & Top Picks

It’s a privilege to share your life with a beloved feline companion. The changes that cats undergo as they pass through middle age into advanced seniority require some lifestyle changes. At some stage, you may need to consider adjusting their...

black and white old cat eats from a plate

15 Vet-Verified Reasons Your Cat Sleeps Under the Bed: With Tips to Manage Anxiety

Do you ever wonder why your cat likes to sleep under the bed? There are actually several reasons why cats like to do this. In this blog post, we will discuss the 15 most common reasons why cats like to...

Cat Sleeping

Is Cooked Chicken Good for Cats with Hyperthyroidism? Vet-Approved Benefits & Tips

Hyperthyroidism can be a heavy diagnosis to get your head around. Once you learn about an overactive thyroid, you realize that certain changes may need to take place with what your cat eats. A vet will likely give you recommendations...

boiled chicken in a pot broth close-up

Is Aglaonema Toxic to Cats? Vet-Verified Houseplant Advice

House plants are a fantastic way to give your home some life, so much so that many people have taken up the role of plant parents, adorning their space with greenery. Aglaonema commutatum, also known as the Chinese evergreen plant,...

Catster_Is Aglaonema Toxic to Cats

Love Cats? So Do We! Join the Catster Community

Stay informed with expert pet care insights delivered straight to your inbox! Discover professional guidance on animal behavior, feeding tips, trusted product picks, and much more.




Sign up for the Catster Email Newsletter

Stay informed with expert pet care insights delivered straight to your inbox! Discover professional guidance on animal behavior, feeding tips, trusted product picks, and much more.