Sebaceous glands sit next to the hair follicles. They make an oily substance called sebum, which keeps the skin surface and the hairs supple and protected [1]. Lumps can grow from these glands.
Oil gland lumps are among the most common skin growths in older dogs, while in cats they are uncommon [2]. Vets sort them into several types: overgrowth (nodular hyperplasia), adenoma, ductal adenoma, epithelioma and adenocarcinoma, and some lumps are a mix of two types [2].
Any new lump on your pet should be checked by your vet. A typical-looking overgrowth cannot always be told apart from a true tumor by its appearance [2], so a lab test is what settles the question [2].
For other kinds of lumps, see lumps and bumps on dogs and lumps and bumps on cats.
Types of sebaceous gland lumps
Sebaceous gland overgrowth (nodular hyperplasia). This is the most common form in dogs, and it is benign [2]. In old animals it is sometimes called senile nodular hyperplasia [1].
- Look: raised, hairless bumps that are pink to yellow, sometimes waxy, and often made of several small lobes. Most are smaller than 5 millimeters, though some reach a few centimeters. Many have a small dip in the middle, and some have an open sore on top [2]. A greasy surface helps set them apart from warts [1].
- Where: there may be one bump or many, anywhere on the body, but the head, chest and belly are common sites [2].
- Who: male dogs of toy breeds are reported more often. Beagles, Cocker Spaniels, Poodles, Dachshunds and Miniature Schnauzers are also commonly affected [2].
Sebaceous gland adenomas. These are benign tumors and one of the most frequent oil gland tumor types in dogs [1][2].
- Look: they can look exactly like an overgrowth, and some are dark in color [2].
- Where: eyelids and legs are common sites [2]. In a large lab study from Portugal, adenomas were often found on the neck and head, and many dogs had them in more than one place [4].
- Who: in that study they were seen more in older dogs and more in females than males, and Cocker Spaniels stood out within their breed [4].
Sebaceous gland epitheliomas. These are about as common as adenomas [1]. Vets class them as low-grade malignant: their main risk is growing into the nearby skin, with occasional spread to a lymph node [2].
- Look: they may have an open sore on top and are often dark in color [2].
- Where: eyelids, head and back are the usual sites [2]. The Portugal study found them mostly on the ears and face [4].
- Who: older dogs, and in that study males more often than females [4].
In general, oil gland tumors in dogs are reported more often in breeds such as Cocker Spaniels, Kerry Blue Terriers, Boston Terriers, Poodles, Beagles, Dachshunds, Norwegian Elkhounds and Basset Hounds [1].
The rare malignant form
Sebaceous adenocarcinoma (carcinoma) is uncommon to rare in dogs [2].
- Look: it is usually a bigger lump, often several centimeters across, and the skin over it is often broken open [1][2].
- Who: Cocker Spaniels, Cavalier King Charles Spaniels and terrier breeds may be at higher risk [2].
- Spread: it can grow aggressively into the tissue around it, but spread to distant organs is rare [1][2].
In cats, both adenomas and carcinomas of the oil glands have been reported. They are rarely seen, usually in older cats, with no known sex or breed pattern [1].
How vets find out what a lump is
Your vet can take a fine needle sample of cells from the lump or a small piece of tissue (a biopsy) for the lab [2]. The type is confirmed when a pathologist looks at the tissue under the microscope [3]. When a lump looks unusual, comes back or behaves more aggressively, vets advise a biopsy or removal for lab testing [2].
How vets treat them
- Overgrowths: because they are benign, they do not always have to come off. A bump can become sore if it is inflamed, for example from rubbing or scratching, and the lobed surface can trap debris and germs; removal may then be discussed [2].
- Adenomas and epitheliomas: these are usually removed with surgery, and the outlook is generally good [3].
- Malignant lumps: your vet will explain the options for removal and any further tests.
- Anesthesia: older dogs with oil gland lumps often have other health problems, so your vet will weigh the risk of any procedure [2].
Your vet will decide whether and how to treat a lump.
At home, as directed by a vet:
- do not squeeze, pick or try to remove a lump;
- stop your pet from scratching or licking a crusted lump in the way your vet advises;
- note the size, place and date of each lump so you can show your vet any change;
- go back for every recheck.
Outlook
Outcomes vary between types:
- Benign adenomas are usually cured once they are fully removed [3].
- Overgrowths often keep appearing, one after another, over a long time, so a dog may need more than one procedure [2].
- Epitheliomas come back at the same spot in a small share of dogs, around 6% in published reports [3].
- The malignant form grows into nearby tissue, although distant spread is rare [1][2].
These are statements about groups of animals. They cannot predict how one pet will do. Your vet can explain what this means for your pet.
When to see your vet
See your vet if your dog or cat has:
- any new lump on the skin [2];
- a lump that is sore, inflamed or scratched [2];
- a lump with an open sore on top [2];
- a lump that grows, changes or comes back after removal [2].
FAQ
Are sebaceous gland tumors cancer?
Many are not. Overgrowths and adenomas are benign, epitheliomas are low-grade, and the fully malignant form is rare [2]. Only a lab test can tell the types apart [2][3].
Does a benign sebaceous lump need to be removed?
Not always. Benign overgrowths do not have to come off unless they cause trouble, such as soreness or inflammation [2]. Your vet will decide.
Why does my dog keep getting new ones?
Oil gland overgrowths often develop one after another over a long period of time [2].
The bottom line
Sebaceous gland tumors are lumps that grow from the skin’s oil glands. They are among the most common skin growths in older dogs and are uncommon in cats. Overgrowths and adenomas are benign, epitheliomas are low-grade, and the malignant form is rare. Because the types can look alike, only a lab test can tell them apart, so have your vet check every new lump.
This article is for general information only and does not replace advice from your veterinarian. If your pet has a new lump, see your vet.
Sources
- Pfannkuche H, Maus J, Engel KM, Schiller J, Schneider MR. Decoding sebaceous gland functions and diseases: insights from domestic animals. Veterinary Research Communications, 2026. Open access, CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC12987846/
- Gustafsson L, Wilson A, Bergvall K. Efficient Topical Treatment of Canine Nodular Sebaceous Hyperplasia with a Nitric Acid and Zinc Complex Solution. Animals, 2024;14(4):570. Open access, CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC10885944/
- Kim S, Chaudhary PK, Upadhayaya S, Seo KW, Kim S. Histopathological and Immunohistochemical Characterization of Sebaceous Adenoma and Epithelioma in Dogs. Animals, 2024;14(10):1457. Open access, CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC11117200/
- Martins AL, Canadas-Sousa A, Mesquita JR, Dias-Pereira P, Amorim I, Gärtner F. Retrospective study of canine cutaneous tumors submitted to a diagnostic pathology laboratory in Northern Portugal (2014-2020). Canine Medicine and Genetics, 2022;9:2. Open access, CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC8875941/