Sudden Black Gums on Your Dog: Harmless Lentigo or Melanoma?
Black spots on a dog's gums can be benign lentigo or dangerous melanoma. Here's how to tell them apart and when to biopsy.
Published 2026-04-19
You lifted your dog's lip and noticed black patches on the gums. Maybe they've always been there, maybe they look new. The question everyone asks: is this normal or something scary?
Two very different conditions account for the vast majority of dark gum spots: lentigo (completely benign) and melanoma (serious oral cancer). Here's exactly how to tell them apart.
What Is Lentigo?
Lentigo is benign hyperpigmentation — a harmless buildup of melanin in the gum tissue. Think of it as the dog equivalent of age spots. It's extremely common in older dogs and in certain breeds:
- ✓Chow Chow (often have fully black gums from birth)
- ✓German Shepherd
- ✓Golden Retriever
- ✓Dalmatian
- ✓Newfoundland
- ✓Mixed-breed dogs with these genes
- ✓Any aging dog of any breed
Key features of lentigo:
- ✓Flat — does not raise above the gum surface
- ✓Uniform — same smooth texture as surrounding gum
- ✓Symmetric — often appears on both sides of the mouth
- ✓Painless — dog doesn't react to touch
- ✓Slow onset — develops over months to years; you can't point to "when it appeared"
- ✓Stable — doesn't change in size or shape
- ✓No bleeding, no ulceration, no bad smell
Lentigo requires no treatment. It's cosmetic. Just note it in your mental baseline of your dog's normal.
What Is Oral Melanoma?
Oral melanoma is malignant cancer arising from melanin-producing cells in the mouth. It's one of the most common oral cancers in dogs and can be aggressive, often spreading to lymph nodes and lungs before detection. Most common in:
- ✓Small older dogs (over 10 years old)
- ✓Breeds with heavy oral pigmentation — Chow Chow, Scottish Terrier, Cocker Spaniel, Golden Retriever, Poodle
- ✓Male dogs slightly more than female
Key features of melanoma:
- ✓Raised — visibly lifted above the gum surface (even slightly)
- ✓Irregular borders — not neatly symmetric
- ✓May bleed — especially after chewing or licking
- ✓Grows — size changes over weeks or months
- ✓One-sided — typically localized rather than bilateral
- ✓May ulcerate — have a wet, raw, or cratered surface
- ✓Bad breath — tumors often have a distinctive odor
- ✓Sometimes dog drops food, shows reluctance to chew on that side, or drools
Side-by-Side Comparison
- ✓TEXTURE — Lentigo: flat, smooth / Melanoma: raised, bumpy
- ✓SYMMETRY — Lentigo: symmetric, both sides / Melanoma: one-sided
- ✓ONSET — Lentigo: slow (months-years) / Melanoma: fast (weeks-months)
- ✓BORDERS — Lentigo: smooth, regular / Melanoma: irregular, asymmetric
- ✓BLEEDING — Lentigo: never / Melanoma: sometimes, especially with trauma
- ✓BEHAVIOR — Lentigo: no impact / Melanoma: may drop food, bad breath, drool
- ✓COLOR — Lentigo: uniformly black / Melanoma: black but may have red, brown, or gray areas
Other Causes of Sudden Dark Gums
Not all dark spots are lentigo or melanoma. Less common causes:
- ✓Bruising (hematoma) — from trauma; usually a single localized spot with known injury history; resolves within 1-2 weeks
- ✓Necrotic tissue — dead tissue from severe infection; dark color with foul smell and dog is visibly unwell
- ✓Certain medications — tetracycline, chemotherapy drugs, and some others can darken gums
- ✓Addison's disease — can cause diffuse gum darkening; also causes weakness, vomiting, weight loss
- ✓Other oral tumors — squamous cell carcinoma, fibrosarcoma; less commonly pigmented but can appear dark
When to See a Vet
Within a week for any of these:
- ✓A new dark spot you've never noticed before
- ✓Any raised pigmented lesion, even if small
- ✓A pigmented spot that bleeds, even a little
- ✓A pigmented spot that's growing
- ✓Dark gums + bad breath + dog dropping food
- ✓Dark gums + dog is acting unwell
Same day if:
- ✓Heavy bleeding from a gum lesion
- ✓Dog is very lethargic, not eating, or in visible pain
- ✓A dark area that's foul-smelling
- ✓Rapid growth in a few days
What the Vet Will Do
For a suspected melanoma: fine-needle aspirate or incisional biopsy for cytology/histopathology, chest X-rays to check for lung spread, lymph node palpation, and sometimes CT scan. Treatment depends on staging — can include surgery, radiation, and a melanoma vaccine (Oncept) for some cases. Early-stage oral melanomas have better outcomes than late-stage — time matters.
For confirmed lentigo: nothing. Reassurance, and maybe a photograph for your records to compare against in the future.
Monitoring at Home
Once you know your dog's baseline, recheck the mouth monthly:
- ✓Lift the upper lip on both sides and look at the gum above each canine
- ✓Check lip margins, tongue, and roof of mouth
- ✓Photograph any pigmented spots with dates — catches growth early
- ✓Note bad breath changes (new stench without new food = worth a vet visit)
Unsure if a spot looks benign or concerning? Upload a photo — our AI can help distinguish lentigo patterns from potentially worrying lesions and suggests whether a biopsy is warranted.
Is It Lentigo or Something Worse?
Upload a photo of the dark area and let AI assess whether it matches benign lentigo or warrants a biopsy.
Disclaimer: This article is for informational purposes only and is not a substitute for professional veterinary advice. Always consult a licensed veterinarian for diagnosis and treatment of your pet's health conditions.
