New Cat Poisons: Hair Dyes, Hair Loss Treatments & Diclofenac

I want to warn you about three emerging and important toxins of cats. I also want you to see the link between these products and how they may be just the tip of the iceberg in household poisonings.

Minoxidil : A Baldness Treatment

Minoxidil has become extremely popular due to its ability to stimulate hair regrowth on the scalp of people. It was originally marketed as Rogaine, but is now available as an over the counter generic in liquid, foam and shampoo forms.

When cats lick even a tiny amount, it causes vomiting, drooling, low blood pressure, severe illness and often death. Because the product is applied to the skin, it can easily come into contact with cats either directly, by licking the area, or even from pillows.

I first discovered this toxin one year ago after a report from the Animal Poison Control Center that you can read here. In their list of the top causes of poisoning deaths in cats, it included a drug I had never heard of.

If I didn’t know about it, it meant many other vets didn’t either, and very few cat owners.

The message is simple: if you use minoxidil in any form, be extremely careful:

  • Clean up areas carefully after use, especially spills or stray drops
  • Do not allow your cat to come into contact with treated areas of skin
  • Prevent access to bedrooms 
  • Clean sheets and pillowcases frequently

PPD: A Hair Dye Ingredient

Para-phenylenediamine (PPD) is a fixative found in many hair dyes and henna temporary tattoos. It causes a deeper, longer lasting and more intense colour. Oral ingestion leads to intravascular hemolysis, rhabdomyolysis, myoglobinuria and acute renal failure. 

In other words, this means massive destruction of red blood cells and muscle cells. The release of their contents into the circulation causes downstream kidney damage. This is the same process you sometimes hear about with overexercise in hot conditions

I only heard about this toxin last week, but I saw a case a year ago that I’m now convinced was caused by it. 

Mimi’s Acute Renal Injury

Mimi’s owners came to me for a second opinion after he was diagnosed with acute kidney failure. The interesting thing is that despite an extensive search for the toxin, it was never found. However, due to the timing, Mimi‘s owners strongly suspected that a hair dye had caused it.

At the time, I conducted a search to the best of my abilities and found no link between dyes and poisoning. The case remained a mystery. Mimi survived only thanks to heroic efforts by his owners and a number of veterinary teams.

Knowledge of the toxicity of PPD is well known in human medical circles, but no documented cases of poisoning exist in animals. It’s likely that the lack of evidence is due to a lack of recognition, not occurrence. Like in Mimi’s case, it’s near impossible to prove a particular toxin causes kidney failure due to the delay between poisoning and diagnosis.

Once again, prevention is about minimising exposure:

  • Use hair dyes and hennas without PPD if possible
  • Use dyes and hennas in a well-ventilated place where your cat cannot join you
  • After completion, clean up any spills and splashes carefully
  • Rinse basins, baths and showers thoroughly since cats often like to lick these areas after use
  • Don’t allow your cat to lick the dyed areas

Diclofenac (Voltaren)

A third common cause of cat poisoning deaths is the human use of potent anti-inflammatories. Once again, the risk is mainly from products applied to the skin. Products like Voltaren gel contain diclofenac, which even in small quantities will cause kidney failure.

Cats are likely to be poisoned either by licking the treated areas, or getting spilt product on their paws or coat. In addition to the methods above, prevention should also include covering the treated areas with clothing and keeping the products in a secure place.

The Common Link

All three of these toxins show us how susceptible cats are to household poisoning. This is for three reasons:

  1. Cats are naturally inquisitive and will seek out and investigate new things
  2. Cat seem inherently sensitive to a wide range of chemicals
  3. Anything that contacts the outside of a cat will invariably be licked off and swallowed

The third point means we should add a final form of prevention: if anything not known to be safe gets on your cat’s coat or paws, you will need to give them a bath. This is not a decision taken lightly, but it may be life-saving.

Moreover, I would be careful about any medicines, dyes or other household chemicals, regardless of whether they contain diclofenac, minoxidil or PPD*. If we are learning one thing, it’s that cats will show us just how toxic a chemical can be.

Have something to add? Comments (if open) will appear within 24 hours.
By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. Meet his team here.


Anuradha, S., Arora, S., Mehrotra, S., Arora, A., & Kar, P. (2004). Acute renal failure following para‐phenylenediamine (PPD) poisoning: a case report and review. Renal failure26(3), 329-332

Tater, K. C., Gwaltney-Brant, S., & Wismer, T. (2021). Topical Minoxidil Exposures and Toxicoses in Dogs and Cats: 211 Cases (2001–2019). Journal of the American Animal Hospital Association57(5), 225-231

* Just look at the ingredient list for a non-PPD containing hair dye for example: how many of these do you think have been tested in cats? Cetearyl Alcohol, Ammonium Hydroxide, Glyceryl Stearate, Ceteareth-20, Toluene-2,5-Diamine Sulfate, Octyldodecanol, Sodium Laureth Sulfate, Ethanolamine, Sodium Cetearyl Sulfate, Fragrance, 2-Methylresorcinol, Resorcinol, Serine, Sodium Sulfite, Oleic Acid, Potassium Stearate, Glycerin, Tetrasodium EDTA, m-Aminophenol, Carbomer, Linalool, Potassium Hydroxide, Citronellol, Ascorbic Acid, Butylphenyl Methylpropional, Linoleamidopropyl PG-Dimonium Chloride Phosphate, Propylene Glycol, Sodium Sulfate, Hexyl Salicylate, 2-Amino-3-Hydroxypyridine, Hydrogen Peroxide, PEG-40 Castor Oil, Disodium Pyrophosphate, Disodium EDTA, Sodium Benzoate, Phosphoric Acid, Behentrimonium Chloride, Dimethicone, Amodimethicone/Morpholinomethyl Silsesquioxane Copolymer, Magnesium Citrate, Magnesium Chloride, Hydrolyzed Keratin, Polyquaternium-37, Macadamia Ternifolia Seed Oil, Panthenol, Isopropyl Myristate, Citric Acid, Phenoxyethanol, Stearamidopropyl Dimethylamine, Isopropyl Alcohol, Sodium Methylparaben, Dicaprylyl Carbonate, Laureth-23, Laureth-4, Sodium Hydroxide, Hexyl Cinnamal, Benzyl Salicylate, Benzyl Alcohol, Limonene, Lauryl Glucoside, Trideceth-5, Salicylic Acid.

3 Replies to “New Cat Poisons: Hair Dyes, Hair Loss Treatments & Diclofenac”

  1. My cat took 2 links off my leg and had put diclofenac gel on them 2 hours prior. Should I be worried. She is still the same as always. Eating a lot and having the zoomies and drinking her normal amount of water. Should I take her to the vet

  2. thank you so much for this informative article. i noticed that my british shorthair likes licking the bath after i’ve showered (shower is over the bath) so i’ll be extra careful to rinse any residual shampoo/conditioner/cleanser away.

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