Apocrine Cysts: Blue Lumps on the Skin & Ears of Cats

Apocrine cysts are just another strange thing cats can grow. When my foster Elise had bluish, blackish lumps in a few places of her body, I was concerned. I had never seen something like that before. My searches for more information or pictures of what I was seeing turned up nothing. It turns out, she has cysts related to the sweat glands. Cysts that grow from these glands (and glands related to them) look bluish, purplish, or even black. One type can appear on the skin, and the other in the ears. Many times, I see black and think blood and worry, but these cysts are often benign. We’ll take a look at what they are and when you may need to have them removed.

Apocrine Cysts Have Lots of Names

After looking up the name my veterinary dermatologist gave me, I found a bunch of other names. Articles and studies will even call them something and list other names in parenthesis. I wanted to list some of the names here to help people searching for various terms still find this info.

Names for Apocrine Cysts on the Skin

  • Apocrine gland cysts
  • Apocrine cystomatosis
  • Cutaneous apocrine cystomatosis
  • Cystic apocrine gland dilations
  • Cystic apocrine gland hyperplasia

Names for Apocrine Cysts in the Ears

  • Ceruminous cysts
  • Ceruminous cystomatosis
  • Ceruminous gland hyperplasia
  • Ceruminous adenoma
  • Apocrine cystadenomatosis

What Are Apocrine Glands?

Apocrine glands are one of two types of sweat glands. In cats, they’re located in the hair follicles and anal sacs. They don’t produce sweat, but an oily substance used for chemical communication (territory marking, mating status, etc.).

Sweat glands called eccrine glands actually produce sweat. They’re located on the paw pads and nose. (You’ve probably noticed your cat’s paw pads are a little moist when they’re nervous, like at the vet or in the car.) Cats rarely grow cysts on their paw pads or nose, so we won’t discuss them further in this post.

The ear canal is home to ceruminous glands, which are a modified apocrine gland. The substance they secrete combines with oil from the sebaceous glands to create ear wax.

Two Main Cyst Types

Balinese cat
Gorgeous Capote

There really isn’t a ton of info on apocrine cysts and ceruminous cysts because they are extremely rare, representing only 3% of skin tumors in cats. What we do know is they are most common in middle-aged to older cats. What causes them? We really don’t know that either. They could be a result of aging or a congenital condition, meaning an abnormality the cat was born with. Ceruminous cysts are slightly more common in some breeds, specifically Abyssinian and Persian, but scientists are cautious to link it to genetics. I have seen hundreds of cats and have only seen ceruminous cysts one time in the ears of a Balinese named Capote.

Apocrine cysts will appear as raised, bluish, purplish lumps on the skin. The size and color really stand out compared to other growths which may not have a color. My foster Elise has them in many places, but they are most noticeable on the chin, butt, and paw.

Ceruminous cysts grow in the ear, and are also bluish/purplish in color.

Usually Benign, But …

The cysts are most often benign, but apocrine adenocarcinoma is a malignant tumor of the sweat glands. Although it can be hard to distinguish, the lumps are usually more ulcerated and inflamed compared to cysts. In fact, a tumor was found under one of Elise’s cysts. We won’t know what type of tumor it is until it’s removed surgically.

Ceruminous adenocarcinoma is rare but can happen, and again the signs would be more ulcerated and possibly bleeding lesions in the ear.

A veterinary dermatologist who looks at growths all the time is the best person to examine lumps and bumps. They will advise if it makes sense to aspirate any questionable lumps to check for cancerous cells.

Treatment for Apocrine Cysts & Ceruminous Cysts

Cat in cat bed
Elise’s apocrine cysts annoy her, but overall she seems pretty happy.

Apocrine cysts are filled with a dark fluid. While it can be drained, the cysts will refill with fluid again. The only way to remove these cysts is by cryosurgery aka freezing them off. Read more about this method here. Removal is the right move if the cysts cause problems or discomfort, but since they’re benign and usually not an issue, they’re often left alone. Keep in mind that if removed, they likely will come back. For this reason, it’s best to strategically time surgery so the cat doesn’t need multiple removal surgeries close together.

Keep in mind that there are very many conditions for cats that can show up on their skin. Here is a very good breakdown of a variety of growths that can appear on the skin. You can also read up on allergies, a not-very-common and always extremely complicated skin issue, in this article I wrote.


Ceruminous Gland adenocarcinoma in a Domestic Persian-Mix Cat (Felis catus), by Mahir A.G. Kubba, Said N. Wafa and Seham A. Al-Azreg, Open Veterinary Journal, 2018.

Neoplastic and Nonneoplastic Tumors by Amy Leblanc, Small Animal Dermatology, 2017.

Tumors of the Skin in Cats and Epidermal and Hair Follicle Tumors in Cats by Alice E. Villalobos, MERCK MANUAL, Veterinary Manual.

By LizsKittyBootCamp

Hi, I'm Liz, and I'm a cat behaviorist who provides advice and insights on cat behavior.

4 replies on “Apocrine Cysts: Blue Lumps on the Skin & Ears of Cats”

Thanks Jake. Like to share rare stuff esp if I have probs finding info about it.

Great information. I just took my cat to the vet for problems with the anal sacs; during the general exam the vet noticed blue/black discoloration on the inside of the ears along with these little blistery, bally, black things. I had never seen it before (i will start looking in my cat’s ears more often), but when i asked the vet if she had ever seen that before, and what caused that in my cat, the vet said gravely, “Yes. It’s food allergies”. Have you ever heard of that as an explanation? The vet didn’t tell me the name of the condition, i just had to search the internet, and yours is one of the very few places to discuss the condition. Thank you!!

I haven’t heard them explained as food allergies before. Typically food allergies come with other symptoms like GI upset and itchiness. Does your cat have other symptoms?

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