Diagnosis and Treatment of Dog Lumps on Skin


"Dog lumps on skin (also called dog skin tumors) can have many causes such as an insect bite that results in an abscess where pus forms under the skin, lipomas (fatty tumors which are usually benign or not cancerous), skin tumors or cysts. Don't rush to judgment and assume that a canine skin bump is cancerous, as many types are benign or not cancerous. The diagnosis will depend on an understanding of if the lump has changed over time, rate of growth, the look and feel and if it is interfering with the quality of your dog's life. That said, 25% of dogs will develop cancer at some point in their life, making it imperative that any unusual scab, bump, lump or sore on the skin be investigated by a veterinarian. The most common type is a mast cell tumor with 20% of all cases (benign and malignant). There is no known way to prevent skin malignancies other than squamous cell cancer which is thought to be caused by sunlight.

The best thing you can do for a dog skin lump is to have a veterinarian take a look. Often the Vet will recommend watching the skin lesion and if it changes in appearance, then do a biopsy or use another diagnostic approach. If required, the tumor can be surgically removed or another type of treatment applied (radiation, chemotherapy)."

Dog Skin Lumps from pustules, crusting and red bumps caused by a bacterial infection (also called Pyoderma).

Causes and Types

Lumps are primarily due to fluid accumulation under the skin. There are multiple reasons why this might occur. In general, causes fall into two categories:

Benign Dog Tumors (not cancer) 

Characteristics of these lumps are no or slow growth. It is possible that they will not change or take years to change. These growths can become large, although they are usually well defined and small.Common types of benign dog skin bumps include:

  • Abscess: this is a cavity in the skin filled with pus.Abscesses are caused by infections, very rarely they can form at the sites of an injections.

  • Sebaceous cysts: pea-sized scas filled with a thick liquid or cheesy substance). These dog lumps on skin are caused by an oil producing gland called the sebaceous gland. If the gland gets blocked it gets enlarged as small as a pen eraser and as big as 2 inches wide. If the cyst opens you will see a white pasty substance come out. These cysts can be removed with surgery and can refill if punctured.

    Sebaceious Cyst on Dog Skin
     Picture of Dog Lump on Skin
    Picture of Canine Sebaceous Cyst

  • Warts: Warts are rough surfaced lumps that are hard, firm bumps that are often the result of a viral infection. They are seen in young and old dogs. Young dogs get warts from a viral infection that are seen around the mouth. Warts in younger dogs go away by themselves.

  • Lipomas:  Canine lipomas are fatty tissue just under the skin surface about the size of a large coin, but could grow to the size of a large ball. They are often seen in middle aged, overweight female or older dogs and tend to appear on the belly and upper legs. Lipoma's are usually seen in Schnauzers, Labs, Dobermans and mixed breeds. It is rare for a lipoma to be cancerous. Sometimes they will develop at the top of a forelimb, making it difficult for the dog to run or walk. If this is the case it will need to be removed with a surgical procedure.

  • Adenoma: these develop in the sebaceous glands of the hair follicles.  There can be multiple adenomas on a dog, particularly in cocker spaniels and miniature poodles. (this is different from the cancerous adenocarcinoma that can also develop in the same location. A similar sounding perianal adenocarcinoma is also cancerous and develops in the tissue of the anus).

  • Pimples/blackheads: Similar to people, dog skin can have the same types of problems. Like humans, you can rid your dog of pimples through cleaning clogged pores and the use of benzoyl peroxide. Another name for pimple is papule which is defined as a small solid rounded bump rising from the skin that is usually less than 1 centimeter in diameter (less than 3/8 inch across). Papules may open when scratched and become crusty and infected. Dermatologists (and other physicians) call any small solid circumscribed bump in the skin a papule, as opposed to a vesicle which contains fluid or a macule which is flat and even with the surrounding skin.
  • Elbow Calluses: Large dogs can get lumps and bumps where their body comes in constant contact with the ground. These lumps are usually calluses or hardened skin. These can be treated by applying petroleum jelly, lanolin or other dog safe softening products.

  • Hives: Hives are often a reaction to something in your dog's environment. Allergic reactions to bug bites or a medication can cause the skin to swell from 1/2 inch to 2 inches. You could try Benadryl in the dosage 1 mg per pound of body weight. If ineffective, see your veterinarian. Another name for hives are Wheals which tend to look like a circumscribed, circular, raised area of skin caused by swelling due to the retention of fluids in the skin tissues (oedema). Wheals are seen at the site of positive skin test reactions when dogs are allergy tested.

Malignant Lumps (cancerous)

These lumps may grow quickly and spread into the skin. These dog skin tumors can grow uncontrollably and metastasize (spread) to other parts of the body. The most common type of are mast cell tumors and occur 20% of the time (benign and malignant types)
  • Mast cell tumor: These types of cells are essentially white blood cells that are used by the body to defend against outside elements that enter your dogs body. For example, an insect bite causes swelling on the skin because of these cells. If the normal mast cell undergoes a malignant change, a mast cell tumor may be produced. They can be malignant or benign and are found in the bone, cartilage, the skin and other tissues. The cells contain histamine which is a chemical released by the dogs immune system.
Mast Cell Tumor
Picture of Dog Lump on Skin Mast Cell Tumor
Dog Mast Cell Tumor Picture on Dog's Skin

  • Neoplasia Nodule: a firm, solid cutaneous swelling up to 1 cm in diameter caused by infiltration of inflammatory or cells that are abnormally uncontrollably growing (neoplastic cells).

 Picture of Dog Lumps on Skin
Picture of a Histiocytoma, a type of Canine Neoplasia or Tumor

  • Squamous Cell Carcinoma: These are flat scaly cells on the outer skin layer. Dogs that have white coats or lightly pigmented skin are predisposed. A contributing factor is sun exposure such as dog that frequently basks in the sun while lying on its back.

Dog Skin Pimple
 Dog Lump on Skin Photo Pimple
Photo Dog Lumps on Skin Pimple or Papule

  • Haematoma: a cavity in the skin filled with blood. Haematomas are usually caused by trauma or injury.

  • Melanoma: Dog skin melanomas form in pigmented skin cells.

  • Fibrosarcomas: Dog skin tumors that form in fibrous tissue.

  • Hemangiopericytomas: canine skin tumors that form near blood vessels.

Keeping Track

Janet Tobiassen Crosby, DVM in Your Guide to Veterinary Medicine has some excellent advice for keeping track of dog lumps on the skin. She recommends the following approach:

  1. Take a piece of wax paper and a felt marker.
  2. Lay the wax paper over the lump. Trace the outer edges of the lump.
  3. Date the wax paper.
  4. Repeat monthly (or shorter intervals, if your vet suggests) to monitor.

Canine Skin Bump or Lump Diagnosis

Your Veterinarian will look at the physical characteristics of dog lumps on the skin to determine a preliminary diagnosis. They will look at the location, duration, firmness, and size of the canine skin lump or bump.

According to Dr. Timothy Fan, your veterinarian will ask several questions about the dog lumps on skin or bumps:

  1. Has the lump appeared suddenly, or has it been there awhile?
  2. Has the lump stayed the same in consistency and appearance or has it changed recently?
  3. Does the lump seem to separate from underlying tissue or is it attached?
  4. Is there only one lump or have you found multiple dog lumps on skin?
  5. Are there changes in your dog's behavior such as eating less, losing weight, vomiting, diarrhea, or lethargy?
Common signs of Dog Neoplasia (tumor)
  1. Abnormal swelling that does not stop growing
  2. Sores that fail to heal
  3. Loss of weight
  4. No appetite
  5. Any bleeding from any part of the body
  6. Strong offensive smell or odor
  7. Trouble swallowing or eating
  8. Reluctance to exercise, low energy
  9. Acting lame or stiff frequently
  10. Respiratory issues, urination issues, defecation issues (trouble going to the bathroom)

To be sure of a diagnosis of dog lumps on skin, the veterinarian will take a sample by using a needle to remove some of lump for study in a laboratory (fine needle aspirate).


Mast Cell Neoplasia
dog lumps on skin
Dog lumps on skin caused by Mast Cell Neoplasia on Sharpei legs

For Lipoma, your Veterinarian will probably watch and wait to see if the identified dog lumps on skin shrink or stop growing. If the lump interferes with your dog's quality of life or is growing, then surgery is used to remove the lump.

Warts in younger dogs will go away by themselves. In older dogs they will need to be removed with surgery if they are causing any kind of problem (bleeding, irritation).

If the dog lumps on skin or bump is malignant, then routine cancer therapy including surgery, radiation and chemotherapy are used. It can be difficult to determine the best treatment option. While cancerous conditions cannot be prevented, overall skin health may improve with homeopathic supplements such as Skin & Coat Tonic, which are formulated to support the systemic health of the skin and C-Caps which promotes cellular health and immune system function.


In general, a dog that has a dog skin growth removed surgically will be active in a few hours after the procedure and will not need a look recuperation period. If chemotherapy is used then the recuperation is longer. If the growth has been completely removed, then there is a good change the growth will not return, leading to an excellent prognosis. Prognosis in general refers is related to the size of the tumor and the ability of the surgeon to completely remove the growth.

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References for Dog Lumps on Skin

Washington State University
What to do if you find a growth on your pet

Sarah Probst
Information Specialist
University of Illinois
College of Veterinary Medicine

Recent Advances in Mast Cell Tumors
K.A. Selting
College of Veterinary Medicine, University of Missouri, Columbia, MO, USA.

Brevitz, Betsy DVM
Hound Health Handbook

Understanding the Language of the Skin
Peter Hill, BVSc, PhD, DVD, DipACVD, MRCVS
The Royal (Dick) School of Veterinary Studies
The University of Edinburgh, Scotland

Date Published:

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