Finding a lump on your dog is worrying, but most skin tumors in dogs are benign, and lipomas and histiocytomas are among the most common.1,2 Still, roughly 1 in 5 to 1 in 3 skin tumors in dogs is malignant, and you can't tell which by looking or feeling.1,2,3 This guide explains the common types of lumps, when to worry, how vets find out what a lump is, and how lumps are treated and monitored.
Have a lump checked by a vet if it:
Show photo: A vet taking a fine-needle aspirate from a small skin lump on a dog
What the Research Shows
- Lipomas are common in older dogs. About 1 in 50 UK dogs (1.94%) is diagnosed with a lipoma each year, and dogs aged 9 to 12 had 17.5 times the odds of dogs aged 3 to 6.8
- Some breeds get far more. Lipomas affected 7.8% of Weimaraners, 7.0% of Dobermanns and 5.2% of Labradors, and dogs at or above their breed's average weight had about twice the odds.8
- Most skin tumors are benign. 21% of skin tumors were malignant in a Danish cancer registry and 37% in a Portuguese lab series; specialist reviews put it at 20% to 40%.1,2,3
- A needle test is reliable. A fine-needle aspirate agreed with biopsy results in 91% of skin and under-the-skin masses.9
- Lumps in puppies are usually harmless. In dogs under 1 year, 87% of skin masses were histiocytomas, and 98.5% of the tumors were benign.10
When to Worry About a Lump on Your Dog
Veterinary oncologist Dr. Sue Ettinger and VCA Animal Hospitals developed the "See Something, Do Something" rule: if a lump is the size of a pea (1 cm) or larger and has been present for a month, it should be aspirated or biopsied.4 Don't wait for a lump to grow; smaller tumors are easier to remove completely.4,11
Signs that a lump needs prompt attention include fast growth, firmness, redness, ulceration or bleeding, and lumps that swell or redden after handling.5,6 But soft, movable lumps aren't automatically safe: some mast cell tumors feel soft and are frequently mistaken for fatty lumps.6
Common Benign Lumps
- Lipomas (fatty lumps): soft, round, slow-growing and movable lumps under the skin, most common in older, larger and overweight dogs and Labradors.5,8 Most can be left alone and watched.5,12 See lipomas in dogs. A rare form, the infiltrative lipoma, grows into muscle and other tissue and is harder to remove.13,5
- Sebaceous and follicular cysts: round lumps filled with thick, cheesy, gray-yellow material. They may burst and discharge material that looks like cottage cheese. Boxers, Shih Tzus, Schnauzers and Basset Hounds are prone.14 Don't squeeze them: a cyst that breaks open under the skin can become inflamed, painful or infected.14 See cysts on dogs.
- Histiocytomas: small, raised, often red and hairless lumps in young dogs, usually under 3½ years old. Most go away on their own within 2 to 3 months.15 See histiocytomas in dogs.
- Papillomas (warts): cauliflower-like growths caused by a virus, common in young dogs, that often go away on their own within weeks to months.16 See warts and skin tags on dogs.
- Sebaceous adenomas: benign gland growths common in older dogs, usually more than 1 cm across.15
Cancerous Lumps
- Mast cell tumors: the most common malignant skin tumor in dogs, typically at 8 to 10 years.15 They can look like almost anything, from a soft lump to a red, itchy bump. Boxers are among the highest-risk breeds, with about 11 times the odds in one analysis.6 Low-grade tumors are often cured by surgery, while high-grade tumors are much more aggressive.6 See mast cell tumors in dogs.
- Soft tissue sarcomas: about 15% of skin and under-the-skin tumors. They can feel soft or firm, and a needle test is needed to tell them from a lipoma.11,17 They tend to come back if not removed with wide margins, but most low-grade tumors don't spread.11,17
- Melanomas: most melanomas on haired skin are benign, but those on the toes, nail beds, lips and in the mouth are often malignant.7,18
- Squamous cell carcinoma: linked to sun exposure on lightly pigmented skin, especially in breeds such as Dalmatians, Bull Terriers, Beagles and Whippets.19
See skin cancer in dogs for more on these tumors.
How Vets Find Out What a Lump Is
- Fine-needle aspirate (FNA): a thin needle collects cells for examination under a microscope. It's quick, inexpensive and often done without sedation. It agreed with biopsy in about 91% of cases in one study, but some samples don't contain enough cells.9,20
- Biopsy: a piece of tissue, or the whole lump, is sent to a pathologist. It's needed for a definitive diagnosis of many tumors and to grade cancers such as mast cell tumors.20,6
- Staging tests: for cancers, your vet may recommend blood and urine tests, chest X-rays, abdominal ultrasound or sometimes a CT scan to check for spread before surgery.17
Knowing what a lump is before surgery matters: suspected cancers need wider margins (often about 3 cm) than benign lumps, and a first surgery that removes too little makes recurrence more likely.20,11
Treatment of Skin Lumps
- Watch and recheck: many confirmed lipomas, histiocytomas and warts need no treatment. In UK practice, only 19% of lipomas were removed.12,15
- Surgical removal: for cancers, fast-growing lumps, and benign lumps that bother the dog, such as a large lipoma in the armpit that limits movement.5,20 Cysts are often cured by removal.14
- Additional treatment: radiation or chemotherapy may be recommended for tumors that can't be removed completely or that are likely to spread.20,17
Monitoring Lumps at Home
Check your dog's skin once a month. Specialists suggest rechecking benign lumps with your vet every 3 to 6 months.4 Keep a simple record: where the lump is, its size (measured with a ruler or calipers, or compared with a coin) and a photo. Tell your vet about any change in size, shape or firmness.5,4 For reader questions about lumps, see the answers below.
Frequently Asked Questions
When should I worry about a lump on my dog?
If it's pea-sized (1 cm) or larger and has been there a month, or it's growing, firm, red, bleeding or changing. Have it checked.
How can I tell if a lump on my dog is cancerous?
You can't tell by look or feel. A needle aspirate or biopsy is the only way to know.
What does a fatty lump on a dog feel like?
Usually soft, round and movable under the skin. But some mast cell tumors and sarcomas feel the same, so have it tested.
Can a lipoma turn into cancer?
Lipomas are benign. The malignant fatty tumor, liposarcoma, is rare and is a different tumor rather than a lipoma that changed.
Do lipomas need to be removed?
Usually not. Removal is considered if one grows quickly, gets very large, or gets in the way of movement.
What is a sebaceous cyst on a dog?
A sac under the skin filled with thick, cheesy material. It may burst. Removal is often curative.
Why does my young dog have a red, round lump?
It may be a histiocytoma, a common benign lump in young dogs that usually goes away in 2 to 3 months. A vet should confirm it.
Do skin tumors in dogs hurt?
Most don't, which is why lumps are often found by touch. Some, like inflamed mast cell tumors or abscessed cysts, can be sore.
Ask Our Team a Question
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Sources and further reading
This article was rewritten and fact-checked on October 15, 2026 against current veterinary references and specialist guidelines:
- Brønden LB, Eriksen T, Kristensen AT. Mast cell tumours and other skin neoplasia in Danish dogs: data from the Danish Veterinary Cancer Registry. Acta Veterinaria Scandinavica, 2010.
- Martins AL, et al. Retrospective study of canine cutaneous tumors submitted to a diagnostic pathology laboratory in Northern Portugal (2014–2020). Canine Medicine and Genetics, 2022.
- Bacon N. Practical review of common skin and subcutaneous tumours in dogs and cats. EVC Voorjaarsdagen, 2013. Conference proceedings hosted by IVIS (full text requires free IVIS login).
- Ettinger S. See something, do something: improving outcomes for pets with cancer. Today's Veterinary Practice, July/August 2017.
- Cornell Richard P. Riney Canine Health Center. Lipomas in dogs. March 2025.
- Veterinary Society of Surgical Oncology. Skin mast cell tumor, canine.
- Villalobos AE. Tumors of melanocytic origin in animals. Merck Veterinary Manual, November 2024.
- O'Neill DG, Corah CH, Church DB, Brodbelt DC, Rutherford L. Lipoma in dogs under primary veterinary care in the UK: prevalence and breed associations. Canine Genetics and Epidemiology, 2018.
- Ghisleni G, Roccabianca P, Ceruti R, et al. Correlation between fine-needle aspiration cytology and histopathology in the evaluation of cutaneous and subcutaneous masses from dogs and cats. Veterinary Clinical Pathology, 2006.
- Kim D, Dobromylskyj MJ, O'Neill D, Smith KC. Skin masses in dogs under one year of age. Journal of Small Animal Practice, 2022. Summarized by BSAVA.
- Veterinary Society of Surgical Oncology. Skin soft tissue sarcoma.
- Royal Veterinary College. VetCompass study explores clinical management and outcomes of lipomas in dogs. July 2020 (summarizing a Veterinary Record study).
- Veterinary Society of Surgical Oncology. Skin lipoma, infiltrative.
- Barnes C, Williams K, Hunter T, Stoewen D. Cysts in dogs. VCA Animal Hospitals, April 2026.
- Villalobos AE. Tumors of the skin in dogs. Merck Veterinary Manual (pet owner version), April 2026.
- Mulherin BL. Papillomas in dogs. Merck Veterinary Manual, November 2024.
- Cornell Richard P. Riney Canine Health Center. Soft tissue sarcomas in dogs. May 2025.
- Veterinary Society of Surgical Oncology. Skin melanoma, canine.
- Veterinary Society of Surgical Oncology. Skin squamous cell carcinoma, canine.
- Villalobos AE. Overview of tumors of the skin and soft tissues. Merck Veterinary Manual, September 2024.
About this article
Last updated : fully rewritten using VetCompass and other published studies, the Merck Veterinary Manual, the Veterinary Society of Surgical Oncology, Cornell, VCA, IVIS-hosted proceedings and the See Something, Do Something program; added the research summary, when to worry, common benign and cancerous lumps, needle aspirates and biopsy, treatment, monitoring, key takeaways and FAQ.
This page is for general information and is not a substitute for an exam by your veterinarian.
