Why does my dog have black spots on its skin? Expert explains causes, what to check for and when you should see a vet

Black spots could mean it's time for a visit to the vet. | Canva/Getty Images

Idly patting your beloved dog on the sofa you separate a patch of fur and see an unusual mark on its skin.

It’s the kind of small detail that’s easy to overlook, but once you’ve seen it, it’s hard not to wonder what it is and whether it’s serious.

While black spots on a dog’s skin can sometimes be harmless, they can also signal a range of underlying issues, from parasites to skin infections and changes in pigmentation.

Read more: How Long Will My Dog Live For 2026? Scientists found these were the average lifespans of 17 popular breeds of adorable dog - including the loving Labrador Retriever

The key to understanding what’s going on lies in recognising the different types of spots, where they appear, and how they develop - as each can point to a different cause and require a different approach.

To help out Dr Tanya Leslie, Veterinary Advisor for Douxo, explains the most common reasons dogs develop black spots on their skin, how to tell the difference between them, and when it’s time to seek veterinary advice.

Here’s her advice.

What could the black spots be?

Black spots can have a wide range of causes, from harmless debris to underlying health conditions. Common possibilities include mud or dirt, flea dirt (a sign of fleas), oily flakes linked to seborrhoea, blocked pores (blackheads), areas of skin thickening and darkening (hyperpigmentation), or, much more rarely, tumours.

How can I identify the cause of the black spots?

To identify the cause, Dr Leslie recommends carrying out the following four checks:

Do they move or come off easily?

If the particles sit in the coat and brush away, they may simply be dirt. However, if they resemble grains of black sand, they could be flea dirt.

A simple wet paper test can help with this - if the specks turn red when smeared, this indicates digested blood and confirms fleas. In these cases, the dog, all other pets in the home, and the home environment need to be treated.

Are they flakes or oily residues?

Brown or dark flakes may be linked to excess oil production (seborrhoea). While some flaking is normal, larger amounts can point to underlying issues such as allergies, infections, parasites or hormonal conditions.

Are the spots fixed to the skin?

If the marks don’t move and appear as small, defined areas, they may be blackheads or other localised skin issues. These are fairly common, but if multiple, inflamed, or changing in appearance, they should be assessed by a vet. Rarely, darker irregular lumps may indicate tumours, which should always be checked promptly.

Is the skin itchy, darkened, or thickened?

Dark patches combined with itching or thickened skin are often a sign of hyperpigmentation caused by ongoing irritation. This is commonly linked to allergies, parasites, or bacterial and yeast infections, and typically develops over time.

What if there’s no itching present?

If your dog isn’t uncomfortable, darkened skin can still occur due to hormonal conditions such as hypothyroidism or Cushing’s disease, as well as breed-related traits or natural changes. These cases often come with other signs, such as hair loss or changes in behaviour, and should be investigated by a vet.

When should I go to the vet?

While some black spots are harmless, others require treatment - and it’s not always possible to tell the difference at home. Any persistent, changing, or unexplained spots should be checked by a vet, who may carry out tests to confirm the cause and recommend the most effective treatment plan.

With the right diagnosis, most skin conditions can be effectively managed with a combination of targeted treatments and supportive topical skincare.

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