Proliferative and necrotizing otitis externa is a rare disease that causes thick crusts on the inside of a cat’s ear flaps and at the opening of the ear canal. A University of Minnesota veterinary dermatology handbook explains that the tissue of the ear flap and ear canal overgrows (proliferation) and parts of it die (necrosis) [1]. A 2025 review of feline immune skin diseases says it affects the ear canals and the inner sides of the ear flaps in cats and kittens [2].
The disease is thought to be immune-mediated, which means the cat’s own immune system damages the skin [2][3].
If your cat has thick crusts, bleeding or sores inside the ear flaps, see your vet.
Which cats get it
The handbook says young cats, often between 2 and 8 months old, are the ones usually affected [1]. The 2025 review adds that cats of any age can get it, with published cases from 2 months up to 14 years old [2], so kittens and older cats can both have it.
No particular breed seems to be at higher risk. Most reported cats were domestic shorthairs, and males may be affected a little more often than females [2].
The cause is not known [2][3]. Researchers have found immune cells attacking the outer skin cells, but not what sets them off [2]. Tests in reported cases have not linked it to common feline viruses such as FIV or FeLV [2].
Signs
- Thick crusts: crusts that stick firmly to the skin and are dark red, brown or black [3], on top of red, raised patches [2].
- Where: mainly the inner sides of the ear flaps and the upper, vertical part of the ear canals, usually in both ears [1][3].
- A blocked ear canal: in some cats, growths and raised patches can fill the ear canal completely [1].
- Other areas: the face, including the skin around the eyes, can also be affected [2][3]. In rare cases the disease spreads over much of the body [3].
Crusty ears in cats have many other causes, including ear mites. For those, see cat ear mites and ear problems.
How vets diagnose it
Vets look at the pattern of the crusts and then confirm the disease with a skin biopsy [2]. A biopsy is a small piece of skin checked under a microscope. The review notes that the sample should keep the crusts attached, because they help the pathologist read it [2].
How vets treat it
The disease usually improves with medicines that calm the immune system, either applied to the skin or given by mouth [3]. Your vet chooses the treatment that suits your cat, and some cats need longer care than others [2].
At home, as directed by a vet:
- apply or give all medicines exactly as prescribed;
- do not pick or pull off the crusts;
- do not put any product in or on the ears unless your vet tells you to;
- watch for bleeding, smell or discharge, and tell your vet if you see them;
- go back for every recheck.
Outlook
What the sources report:
- In some cats the disease goes away without treatment, though this can take more than a year [2].
- The review describes the outlook as generally good, including for crusts away from the ears [2].
These are statements about groups of cats. They cannot predict how one cat will do. Your vet can explain what this means for your cat.
When to see your vet
See your vet if your cat has:
- thick, dark crusts on the inner ear flaps [2][3];
- crusts that bleed or open sores in or around the ears;
- crusts around the eyes or on the face as well as the ears [2];
- discharge or smell from the ears.
See your vet again if the crusts come back, spread, or bleed.
FAQ
Can kittens get it?
Yes. Young cats are the ones most often affected, and cases have been reported from 2 months of age [1][2].
Can dogs get it?
The sources we use describe it as a disease of cats and kittens [1][2]. Crusty ears in a dog need their own vet check.
Is it caused by ear mites?
No cause is known [2][3]. Crusty ears can have other causes; see cat ear mites and ear problems.
Will it go away on its own?
It varies, and no one can promise it. Some cases clear up on their own, but it can take more than a year [2]. See the Outlook section above, and talk to your vet rather than waiting.
The bottom line
Proliferative and necrotizing otitis externa is a rare immune disease of cats that causes thick, sticky dark crusts inside both ear flaps and at the ear canal openings, sometimes on the face as well. Its cause is unknown. A skin biopsy confirms it. The outlook is generally good, and some cats recover on their own after a long time, so see your vet.
This article is for general information only and does not replace advice from your veterinarian. If your cat has thick crusts in its ears, see your vet.
Sources
- Torres SMF. 2.10 Otitis Externa: Dogs and Cats. Small and Large Animal Dermatology Handbook, Vol. 1. University of Minnesota Libraries Publishing, 2025 (CC BY 4.0). https://open.lib.umn.edu/animaldermatology/chapter/otitis-externa-dogs-and-cats/
- Banovic F, Gomes P, Trainor K. Feline immune-mediated skin disorders: Part 2. J Feline Med Surg. 2025;27(4):1098612X251323424. Open access, CC BY-NC 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC12033568/
- Brame BE. Proliferative and Necrotizing Otitis Externa of Cats and Kittens. Vet Clin North Am Small Anim Pract. 2025;55(2):337-361. https://pubmed.ncbi.nlm.nih.gov/39824731/