New skin lump on a dog
Any new skin lump deserves a vet check — most are benign but mast cell tumours and other cancers can look unremarkable, and early diagnosis matters.
In the next 60 seconds
- Photograph and measure the lump.
- Note location, size, and any change.
- Phone the vet for a routine appointment within 1–2 weeks.
- Sooner if the lump is rapidly growing, ulcerating, or the dog seems unwell.
Recognise the signs
- New lump anywhere on the body
- Size, shape, growth rate, firmness vary
- Suddenappearance often inflammatory; gradual often tumour
- Some lumps change in size from day to day
First aid steps
- Photograph and measure the lump.
- Note location, size, and any change.
- Phone the vet for a routine appointment within 1–2 weeks.
- Sooner if the lump is rapidly growing, ulcerating, or the dog seems unwell.
Do NOT
- Do not assume a lump is fatty without confirmation — mast cell tumours can feel similar.
- Do not squeeze or pop.
- Do not apply creams.
When to phone the vet immediately
- Rapid growth
- Ulceration, bleeding, smell
- Mass changing size suddenly
- Dog unwell alongside
When it can usually wait
- Slow-growing soft lumps in older dogs are often benign — but vet review with a fine-needle aspirate confirms; do not skip the appointment.
Common causes
- Lipoma (fatty lump, common, benign)
- Sebaceous cyst
- Wart
- Mast cell tumour (can mimic any lump)
- Other tumours
- Abscess (sudden, painful)
- Insect bite reaction (sudden, transient)
What the vet will need to know
- When first noticed
- Size and growth rate
- Any change in size or appearance
- Photos with date stamps
Aftercare
- Fine-needle aspirate (in-clinic, quick, painless) usually confirms type.
- Excision and biopsy for concerning lumps.
- Monitoring for benign lumps.
Prevention
- Routine grooming with hands-on body checks.
- Annual vet exams catch many lumps early.
Breed-specific notes
- Mast cell tumours: Boxer, Bulldog, Boston Terrier, Pug, Labrador.
- Histiocytomas in young dogs.
Frequently asked questions
Is a fatty lump always benign?
Lipomas are benign, but other lumps (including some tumours) can feel similar. A fine-needle aspirate is the only reliable way to know.
Should every lump be removed?
Not necessarily — confirmed benign slow-growing lumps can be monitored. Suspicious or growing lumps should be removed.
How fast do mast cell tumours grow?
Variable — some grow rapidly, others slowly. The 'changes from day to day' pattern is classic. Early diagnosis allows curative surgery.