Lump on a dog's skin

Recognise the signs

• A new lump or swelling that was not there before
• A known lump that has changed — grown, changed texture, changed colour, or become ulcerated
• A lump that the dog is licking, chewing at, or scratching
• A lump that bleeds or weeps fluid
• Multiple lumps appearing simultaneously
• A lump in or around the mammary gland (in bitches)
• Swollen lymph nodes — firm, rounded, found under the jaw, in front of the shoulder, in the groin, behind the knees
• A lump accompanied by systemic signs (weight loss, lethargy, reduced appetite)

First aid steps

1. 1. Do not panic — the majority of lumps in dogs are benign. However, do not ignore new lumps either.
2. 2. Photograph the lump with a ruler or coin for scale so you can monitor for size changes.
3. 3. Note when you first noticed the lump and how quickly it has grown.
4. 4. Check whether the lump is: soft or firm; fixed to underlying tissue or freely movable; single or multiple; painful when touched; warm or normal temperature; ulcerated or intact.
5. 5. Book a vet appointment — a fine needle aspirate (FNA) is a quick, cheap, minimally invasive procedure done in the consulting room that provides very useful information about the cell type.
6. 6. If the lump is bleeding, apply gentle pressure with a clean cloth until the bleeding stops, then contact the vet.
7. 7. If the lump has recently grown rapidly (doubling in size over days to a week), is on a mast cell breed, or is ulcerated — phone the vet for an appointment this week rather than waiting.
8. 8. Do not attempt to squeeze, lance, or remove the lump at home.

While transporting to the vet

• No special transport measures required unless the lump is bleeding significantly.
• For actively bleeding lumps: apply clean gauze and gentle pressure and proceed to the vet.
• Bring photographs showing the lump's progression over time if you have them.

When it can usually wait

• A small, soft, freely movable, slow-growing lump in an older dog that has been stable for months and previously assessed by a vet as a lipoma
• Small warts in a young dog that are not bothering the dog and are known viral papillomas
• Histiocytoma in a dog under 3 that a vet has assessed and confirmed — monitor for 3 months for spontaneous resolution

Common causes

• Lipoma — benign fatty lump, most common soft tissue mass in dogs; soft, movable, under the skin
• Sebaceous cyst — blocked skin gland; firm to fluctuant, may have a white-yellow toothpaste-like discharge if ruptured
• Wart/papilloma — viral (canine oral papillomavirus), typically multiple small cauliflower-like lesions in young dogs; often resolve spontaneously
• Histiocytoma — fast-growing red raised dome in dogs under 3; usually resolves within 3 months
• Mast cell tumour (MCT) — the great imitator; can look like any other lump; variable behaviour from benign to highly malignant; Grade 1, 2, or 3
• Soft tissue sarcoma — arises from connective tissue; often deep, firm, invasive locally
• Perianal adenoma/adenocarcinoma — around the anal area; common in uncastrated males
• Abscess — painful, warm, fluctuant; often from a bite wound, grass seed, or foreign body
• Haematoma — blood blister from trauma, especially ear flap (aural haematoma)
• Lymphoma — enlarged lymph nodes under the jaw, in front of the shoulder, behind the knee
• Mammary tumour — in unspayed or late-spayed bitches; 50% malignant in dogs

What the vet will need to know

• When did you first notice the lump?
• Has it grown? If so, how quickly?
• Is it soft, firm, or fluctuant?
• Is it freely movable or fixed to underlying tissue?
• Is it painful when touched?
• Is it ulcerated, bleeding, or discharging?
• Does the dog pay attention to it — licking, chewing?
• Any other lumps elsewhere?
• Dog's age, breed, sex, and neutered status
• Any previous lumps and results of any testing

Aftercare

• If FNA is inconclusive and clinical suspicion remains: surgical excision with histopathology is the gold standard.
• After lump removal: follow wound care instructions — keep the site clean and dry, use the Elizabethan collar to prevent licking.
• Attend suture removal at 10–14 days.
• Await histopathology results — these tell you the exact tumour type and whether surgical margins were clean.
• For mast cell tumours: staging, grading, and margin assessment determine whether further treatment (oncology referral, radiation, chemotherapy) is needed.
• Dogs with a history of MCT should have all new lumps tested promptly.

Prevention

• Monthly at-home lump checks as part of grooming — run your hands over the entire body, checking under the coat.
• Spay bitches early to reduce mammary tumour risk significantly (before the first season reduces risk to near zero).
• Castrate male dogs to reduce perianal adenoma risk.
• Annual vet health checks which include physical examination of the skin and lymph nodes.
• Prompt treatment of skin infections and bite wounds to prevent abscess formation.
• Sun protection for dogs with pink skin and white coats in sunny weather — squamous cell carcinoma risk.

Breed-specific notes

• Boxers: exceptionally high risk for mast cell tumours — all lumps must be tested.
• Staffordshire Bull Terriers and Bull Terriers: high MCT risk.
• Golden Retrievers: very high overall cancer incidence including MCT, histiocytic sarcoma, and lymphoma.
• Labrador Retrievers: common lipomas but also MCT — test all lumps.
• Weimaraners: mast cell tumour risk above average.
• Beagles: above-average MCT incidence.
• Shar Pei: cutaneous mucinosis creates unusual skin texture but also has cancer predisposition.
• Flat-coated Retrievers: exceptionally high cancer risk including histiocytic sarcoma — monitor closely.

Frequently asked questions

Related topics

• Dog with a swollen muzzle or face