A dark spot in your dog’s mouth:natural pigment or melanoma

Why dogs have dark spots in their mouths

The colour of the lining of the mouth, like the colour of the skin and nose, depends on the pigment melanin. Many dogs have plenty of it in the mouth too: the gums, lips, palate or tongue may be entirely black, grey or bluish, or covered in patches of different shapes. This is a natural feature, not a disease.

In Chow Chows and Shar Peis a blue-black tongue is a breed trait. Spotted gums and tongues are seen in many other breeds and in crossbreeds. Natural pigment has usually been there for a long time: owners often notice it by chance, the first time they look carefully into their dog’s mouth.

Things lying on the teeth rather than in the lining can look dark too: brown or black plaque and tartar at the gum line. This is covered in Yellow, brown and black teeth in dogs. And a dark red or purple patch after an injury may be a bruise: it usually fades within a few days — if it does not, show it to a vet.

How to tell natural pigment from a worrying spot

You cannot make a diagnosis at home, but you can notice whether the spot is changing and what it looks like. Here is a guide:

What is oral melanoma in dogs?

Oral melanoma is a malignant tumour of the pigment cells (melanocytes). In dogs it is one of the most common malignant tumours of the mouth, and it is found more often in middle-aged and older dogs. It can arise on the gums, lips, cheeks, palate or tongue — on dark and on pink lining alike.

Melanoma is serious for two reasons. It grows into the surrounding tissues, including the jawbone, so nearby teeth may become loose. And it can spread (metastasise) to the lymph nodes under the jaw and to the lungs.

In the early stages the tumour may not bother the dog at all: it eats and plays as usual. Bad breath, blood in the saliva, drooling, difficulty eating or swelling appear later. So waiting until the spot “starts causing problems” is not a good idea.

Melanoma can be pink — and a growth is not necessarily melanoma

Some melanomas contain no pigment (they are called amelanotic) and look like a pink or reddish growth, similar to overgrown gum. So a pale colour is no reassurance: a pink lump needs the same check as a dark one.

The reverse is also true: not every growth in the mouth is melanoma. A growth on the gums may be gingival hyperplasia (overgrowth of the gum), an epulis, a papilloma or another tumour, and benign growths can be pigmented too. They cannot be reliably told apart by eye. More on the Growth or lump on the gums page.

How to photograph and monitor a spot at home

Photos are the most reliable way to notice change, because memory lets you down here. This is what I suggest:

• take photos in daylight or with your phone’s torch so that the spot is sharp;
• place a ruler or a coin next to it to show the size;
• photograph from the same side and at the same angle, and note the date;
• repeat the photos during your monthly mouth check and compare them with the earlier ones.

Monitoring is only appropriate for a long-standing flat spot that is not changing. Do not watch a new spot, or one with any of the signs listed above, for months — show it to a vet soon.

How to examine your dog’s mouth calmly and what else to look for is explained in How to check your pet’s mouth at home.

1. 1The gum line. Pink with an even edge. A red line, swelling or blood is a reason for a check-up.
2. 2Plaque and tartar at the gum line. Yellow-brown deposits collect most on the big upper cheek teeth.
3. 3Canine tips and the big upper cheek tooth. Chips, cracks, a pink or dark dot where a tooth has broken.
4. 4Tooth colour. A pink, grey or brown tooth may have a dead pulp.
5. 5Incisors. Are they all there, and are any loose?
6. 6Cheeks, palate and tongue. Ulcers, growths, new dark spots, stuck sticks or bones.
7. 7Face and jaws. Swelling under the eye or along the jaw, asymmetry, pain on touch.

How a suspicious spot is checked

Neither a photo nor the naked eye can tell melanoma from pigment. So the check goes step by step:

1. 01

   In-clinic consultation

   I assess the spot — its size, firmness and edges — the teeth nearby and the lymph nodes under the lower jaw, compare it with your photos and explain what is needed next.

2. 02

   Examination under anaesthesia and X-rays

   Dental radiography shows whether the bone and tooth roots are involved. A CT scan may be needed to plan surgery.

3. 03

   Biopsy

   I take a tissue sample for histopathology, that is, examination of the tissue under a microscope — this is what establishes the diagnosis. A smear of cells (cytology) alone may not be enough.

4. 04

   Staging

   If the tumour is malignant, checks are made to see whether it has spread: the lymph nodes are examined and X-rays or a CT scan of the chest are taken.

5. 05

   Treatment plan

   I explain the results and the treatment options; where needed, the plan is put together with a veterinary oncologist and surgeon.

How oral melanoma in dogs is treated

Treating melanoma is a team effort: a veterinary dentist or surgeon, a veterinary oncologist and, where needed, a radiotherapy specialist. The plan depends on the size and location of the tumour, whether it has spread, and the histopathology results.

Surgery is usually the basis: the tumour is removed together with a margin of healthy tissue, and this not uncommonly means removing part of the jaw. Depending on the stage, the oncologist may suggest radiotherapy, immunotherapy or other methods. How biopsy and removal of growths in the mouth work is described on the Oral tumours page.

It is impossible to promise an outcome in advance, and I do not do so. But a small tumour is generally easier to remove with an adequate margin than a large one, so it is best not to delay with a suspicious spot.

Frequently asked questions