Why Is My Black Cat’s Coat Turning Red-Brown?

Genetics may determine the basic colour of the cat, but other factors can affect the intensity or variation of the colour. These factors can be environmentally determined, as in the area we are about to discuss.

Key points

  • Rusting is a condition in which the coat of a black cat turns reddish/brown.
  • Tyrosine is an amino acid necessary for melanin, which is a pigment in the skin and hair of cats.
  • The current recommended feline dietary concentration is 4.5 g tyrosine for optimal growth.
  • Experiments showed that these levels were not sufficient to maintain a black coat. An aromatic amino acid concentration > or =18 g/kg is recommended for the prevention of visually discernible red hair in black-coated cats.
  • Animal products, such as meat and fish, contain tyrosine.

Some interesting results were found from experiments regarding feline dietary tyrosine nutritional requirements and the effect on black cat’s coat colour. Diets deficient in tyrosine caused the cat’s hair to change from black to reddish-brown in cats and due to a reduction in melanin in the hair.

What is tyrosine?

Tyrosine is an amino acid that the cat synthesises from phenylalanine (another amino acid). Amino acids are the building blocks of protein. Tyrosine is necessary to make melanin, the major pigment in cats skin and hair; it gives us wonderful colours. If you can’t make tyrosine because you are missing the right enzyme, you don’t make as much melanin.

Albinos cannot produce this enzyme, and as a result, melanin cannot be produced, and you end up with the pale skin and hair of the albino. Overactivity of the enzyme can produce the opposite effect, with large areas of highly pigmented skin/hair or it can be associated with the nasty tumours on the skin (melanomas).

Tyrosinase is the action of the enzyme tyrosine on melanin, which causes a complex series of biochemical changes. Tyrosinase is also thermally liable (temperature-sensitive).

A quick side note:

Cats of the Himalayan series (colour points, minks, sepias (semi-albinos)) have heat-sensitive tyrosinase. Normal tyrosinase converts the amino acid tyrosine into melanin (pigment). In Himalayan cats with this enzyme that denatures at normal body temperatures, the colour forms only on the colder extremities of the body (legs, tail ears, face). This is why Siamese cats get darker in winter and paler in summer. If you put socks on your Siamese for several weeks, it would end up with white markings on its feet. The full pigmentation allele for the cat is (C/-). The Burmese cat or sepia cat allele (cb/cb) has slightly thermo-liable tyrosinase, the mink cat or Tonkinese allele (cb/cs) has slightly more thermo-liable tyrosinase, and the colour point or Siamese (cs/cs) has, even more, thermo-liable tyrosinase.

Then there are the true albino cats, which are lacking in the enzyme. The blue eye white albino cat (ca/ca) and the pink or red-eyed white Albino cat (c/c). All these alleles are found on the same locus, and all interact with the enzyme tyrosine. Lack of the enzyme tyrosine is also related to the grey hair both humans and cats get as we age.

The experiments

The current recommended feline dietary concentration is 4.5 g tyrosine plus 12 g phenylalanine/kg amino acids for growing kittens to ensure maximum growth rates and nutritional balance in the kitten’s diet. However, several experiments have shown that it is not sufficient in retaining a black cat’s coat colour.

Results from the studies with cats fed diets with the above aromatic amino acid quantities, and lower show that these levels are not sufficient to maintain a black cat’s, rich black coat and a greater level than this are needed. Black cats on diets deficient in phenylalanine + tyrosine found that their lovely black coat colour changed to a reddish-brown. This was due to a reduction in the melanin (pigment) in the hair, a decreased total melanin concentrations of tyrosine in plasma. Reddish hair colour or rusting was induced in cats fed tyrosine-deficient diets for six months and in black kittens born to queens that were fed tyrosine-deficient diets during their pregnancy.

Maintaining the black coat colour:

The cat and kittens black hair colour was maintained and/or restored by diets containing a high concentration of tyrosine. Cats fed diets with “..<16 g phenylalanine + tyrosine developed ‘red hair.

We confirmed the anecdotal reports that the black hair of cats can change from black to reddish-brown. An aromatic amino acid concentration > or =18 g/kg is recommended for the prevention of visually discernible red hair in black-coated cats. Dietary concentrations >18 g total aromatic amino acids/kg diet promote a greater ratio of PTCA: total melanin in the hair. ” (Anderson et al., July 2002). Cats needed to ingest more than 18g per kg of phenylalanine + tyrosine to maintain or restore a black cat or kittens rich coat colour.

Levels less than 16g resulted in reddish hair colour on the black cat.

Not mentioned in these studies is what happens when a cat ingested too much tyrosine. Anecdotal evidence suggests that the cat’s coat will darken more than it should (e.g. a chocolate cat may become almost black). It is worth thinking about. So, are we feeding enough Tyrosine in our cat’s diets and how much is too much?

Other factors

Without going into too much detail on the complex relationship of the cat’s organs, vitamins, amino acids, below are just a few factors that could be affecting melanin.

Copper deficiency:

One of the early signs of copper deficiency in cats is a loss of hair colour (achromotrichia) as well as a change in the texture of the hair. The reason for the colour change is an alteration to the metabolism of tyrosine. Copper helps tyrosine work as a pigment factor.

Zinc excess:

Too much zinc in the diet may cause a copper deficiency, which, in turn, can cause an iron deficiency. As a result of the copper deficiency, you end up with the above.

Thyroid, kidneys, and liver:

These three organs can also affect coat colour, and all interact with tyrosine. The liver metabolises tyrosine, which is necessary for the synthesis of thyroxin, a hormone produced by the thyroid glands.

Should I just give my cat tyrosine if its coat is turning reddish?

Before you rush out and start adding things to your cat’s diet, please check with your veterinarian first. Many other factors can influence a cat’s colouring. Never supplement your cat’s diet without consultation with your veterinarian.

What you can do:

Feed a high-quality diet with meat as the main ingredient. Learn how to read pet food labels and always check the ingredients panel. The main ingredient will be listed first, followed by the second, third, and so on. Look for cat food which lists meat as the first ingredient.


  • Cats with liver, kidney or thyroid disease
  • Pregnant cats
  • Cats with a malignant melanoma
  • Any cat has a serious illness or is on medication

Please remember always consult with your veterinarian before giving your cat any supplements.


“Red hair in black cats is reversed by the addition of tyrosine to the diet. “MorrisJG, Yu S, Rogers QR. Department of Molecular Biosciences, School of Veterinary Medicine, University of California, Davis, CA, USA. Cats J Small Anim Pract 2001 Apr;42(4):176-80

“Effect of low levels of dietary tyrosine on the hair colour of cats.” Yu S, Rogers QR, Morris JG. Department of Molecular Biosciences, School of Veterinary Medicine, University of California, Davis 95616, USA. J Nutr 2002 Jul;132(7):2037-42 Cats require more dietary phenylalanine or tyrosine for melanin deposition in hair than for maximal growth.

“Sensory Neuropathy in Cats maintained on Phenyl-Alanine/Tyrosine Deficient Diets”. P.J. Dickinson, P. Anderson, D.C. Williams, L.D. Tripp, G.D. Shelton, R.A. LeCouteur. School of Veterinary Medicine, University of California, Davis, CA, and University of California-San Diego (Shelton), La Jolla, CA. Various microbiology texts.