Black Spots on a Dog’s Skin: Causes, Diagnosis, and Best Treatments


Did you notice black spots on your dog’s skin? He might have acanthosis nigricans, a skin pigmentation disorder that is classified into two different types: primary and secondary.

What is primary acanthosis nigricans in dogs?

The primary type of this disorder only occurs in Dachshunds and is characterized by dark and thick skin patches. The skin firms up so much that it somehow looks like elephant skin. The condition is hereditary and does not require any treatment unless bacteria or yeast occurred.

Although it is a genetic disorder, a Dachshund with acanthosis nigricans is not born with the dark patches on its skin. This only appears after a few months or once the dog turns one year old.


What is secondary acanthosis nigricans in dogs?

The other type of this skin disorder can occur in all dog breeds. More often than not, it is a sign of an underlying disease. A common underlying problem is severe skin allergy. You will know it is a case of allergy if the spots are on the armpits.

It can also be a symptom of irregularities in a dog’s endocrine system and can occur when a dog has an overactive thyroid, has elevated levels of the cortisol hormone, or he is suffering from hormone disorders. In some dogs, it happens because of obesity and weight issues.

There are many possible causes to secondary acanthosis nigricans in canines. Aside from allergic reactions, the hormonal imbalance and other types of skin infections can leave the skin inflamed and eventually darker.

When to See a Veterinarian

A dark patch on your pet’s skin should be checked by a doctor if it comes with other symptoms. If your pet is starting to lose his fur and if he has bumps that have fluid inside, you might need to see the vet immediately because it might be a severe skin allergy. In some dogs, the skin also looks crusty and it can even bleed.

How the Canine Acanthosis Nigricans is Diagnosed

Aside from a physical exam, the vet will do a skin surface cytology. There are various ways to obtain a sample for the skin cytology. With impression smears, your vet may press and remove a scotch tape on your pet’s skin.

This goes under a microscope, where the vet is able to see any organisms that might be causing your pet’s disorder. There might be yeast or parasites on your dog’s skin surface. Skin testing or intradermal allergy testing should be done to diagnose the allergy. If it’s hypersensitivity, your vet will recommend an elimination diet to identify the allergen.

How to Prevent Canine Acanthosis Nigricans

While the primary type cannot be avoided, the secondary type of acanthosis nigricans can be prevented. Obesity, for example, is one of the causes of getting dark spots. Pet owners should not only give healthy foods to their pets, they also need to make sure the portions are appropriate for their pet’s size and age.

Exercise is also important for dogs, as it prevents weight problems. Make sure your pet gets his daily walk. A few minutes each day will be enough to keep those joints healthy. The lack of exercise in dogs can lead to obesity.

If your pet has a history of being allergic to certain food items, be careful in giving him treats. The common causes of allergies for dogs are wheat, dairy, and beef. Aside from food allergies, dogs can also suffer from environmental allergies and flea allergy dermatitis.

Treatments for Black Spots on a Dog’s Skin

The treatment for hyperpigmentation in canines takes months and even one year, depending on the condition. The diagnosis itself can take some time so patience is really important on the part of the pet parent. If it’s an allergy, you have to work hand in hand with your vet to identify what’s causing the hypersensitivity.

Antibiotics can be given, depending on the symptoms shown. There are shampoos specially formulated for dogs with hyperpigmentation that can be used twice or thrice a week or as per the advice of a veterinarian.

If the dark spots are due to a severe skin allergy, a vet may prescribe drugs like antihistamines and corticosteroids. These medications are effective in reducing itchiness. Zyrtec and Benadryl are the most common medications that are safe for dogs.

While you can easily purchase these medications over the counter, don’t administer them without consulting your veterinarian. Your vet has to confirm first if it’s a case of atopic dermatitis or something else. There is also a limit in giving these drugs to dogs because these are not meant for long-term use.

An itch-relief shampoo is the best for dogs with intense allergies. Ask your vet about a mild shampoo for your dog. He or she will likely recommend shampoos made of natural ingredients, such as oatmeal and tea tree oil.

Are All Black Spots Acanthosis Nigricans?

No, your dog may be suffering from another type of skin disorder. A dog with lentigo may also have age spots which are characterized by small black dots on different areas of the body. This kind of disorder is characterized by an overpopulation of the pigment molecules.

You don’t need to see a vet to address lentigo since it not really painful, but still, keep an eye for signs of discomfort. Only your vet can confirm if this is actually canine acanthosis or simply lentigo. This is genetic and Dachshunds are also prone to it. Similarly, breeds like the Vizslas and Weimaraners usually have it in the nose area.

Lentigo can occur anywhere on the body. It could be on the armpit, so some mistaken it for allergy. Mostly, it develops on the abdominal area and the spots appear in clusters and in different sizes.


All dogs can get dark patches on their skin and this is often a result of skin allergies and hyperpigmentation. In some cases, the dark patches are not really painful so there is nothing to worry about.

But in case you notice something strange with your dog like him starting to lose hair on parts of his body, don’t hesitate to visit the vet to have him checked. It will be helpful if your vet gets to see it in person, so he or she can perform the right skin tests.


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