Why Is My Dog's Skin Turning Black? 7 Hyperpigmentation Causes in Dogs

If your dog's skin is turning dark, you may be wondering what may have caused such a drastic change. Veterinarian Dr. Ivana shares several varying causes of hyperpigmentation in dogs.

Why Is My Dog's Skin Turning Black? 7 Hyperpigmentation Causes in Dogs
If your dog's skin has turned black, please consult with your vet for diagnosis and treatment.

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Why Is My Dog's Skin Turning Black?

If your dog's skin is darkening to the point of almost becoming black, you're likely concerned about such a drastic change and may be wondering what's going on. Can a dog's skin really change color?

To answer this question we must first assess what a dog's normal skin color looks like. Because a dog's skin is covered, to a great extent, by copious amounts of fur, it's not always easy to be familiar with the normal color so as to readily discern any changes.

What we know is that generally, we may find pink skin in dogs with light-colored coats, while dark brown-to-black skin is commonly found in dogs blessed with dark black and tan coats (as often seen in Rottweilers and Dobermans).

Mottled skin is instead commonly seen in Dalmatians, while a grayish-blue hue may be seen in the Weimaraner, a dog breed affectionately nicknamed the "grey ghost."

A dog's skin color may vary greatly on an individual basis keeping into consideration factors such as breed, age and coat color genetics.

Sometimes, a color change in your dog's skin may stem from an underlying dermatological condition. If you notice one day that your dog's skin has darkened, it's important that you consult with your veterinarian so as to rule out some medical causes.

In this article, veterinarian Dr. Ivana Crnec, a licensed graduate of the University Sv. Kliment Ohridski’s Faculty of Veterinary Medicine in Bitola, Republic of Macedonia, will cover the following topics:

  • What is hyperpigmentation in dogs?
  • Several reasons why a dog's skin darkens
  • The difference between primary and secondary hyperpigmentation
  • Seven causes of hyperpigmentation in dogs
  • Diagnosis and treatment for the darkening of a dog's skin
The Mexican hairless dog is equipped with a naturally dark skin for protection from the sun

Understanding Hyperpigmentation in Dogs

Is your dog suddenly developing dark skin patches? Is he losing hair around the darkened areas? If you answered yes, you are probably dealing with acanthosis nigricans or, more simply, hyperpigmentation.

Hyperpigmentation in dogs looks scary, but in most cases, it is easily treatable. By using the right approach, this skin issue can be reversed. In a nutshell, here's all you need to know about hyperpigmentation in dogs.

What Is Hyperpigmentation in Dogs?

Hyperpigmentation in dogs is defined as “increased pigmentation of cutaneous structures, including skin and hair.” It includes:

  • Melanoderma (increased pigmentation of the skin)
  • Melanotrichia (increased pigmentation of the hair)

What's the Purpose of a Dog's Skin Darkening?

Hyperpigmentation or skin darkening is not a disease. Instead, it is a side effect of skin inflammation.

When attacked (in this case by inflammation), the skin responds by making more melanin (pigment), which results in darkening. Simply put, more melanin means more intense coloring.

In other words, hyperpigmentation in dogs is a protective mechanism. Have you ever noticed how hairless breeds (such as Mexican Hairless and Chinese Crested) have darker skin than hairy breeds?

The reason is better protection. The skin of hairless dog breeds is more exposed to the elements, and the increased melanin presence (dark skin) has a protective role.

Are There Different Types of Hyperpigmentation?

Hyperpigmentation in dogs can be classified based on several features. For example, based on distribution, there are three forms:

  • Localized
  • Multifocal
  • Generalized

Primary and Secondary Hyperpigmentation

Hyperpigmentation in dogs can also be genetic or acquired. Here is a closer look a the causes of primary (genetic) and secondary (acquired) hyperpigmentation.

Primary Hyperpigmentation

Primary hyperpigmentation is a breed-specific condition. Typically, it occurs in Dachshunds, and they start showing darkened areas by the time they are one year of age.

Secondary Hyperpigmentation

Secondary hyperpigmentation is not breed-specific. It can develop in all dogs, regardless of age, breed and sex. Secondary hyperpigmentation can develop in all dogs and can result from many causes—from natural aging to endocrine conditions to cancer.

Did you know? Pomeranians are prone to a skin condition known as "black skin disease."

What Causes Hyperpigmentation in Dogs? 7 Potential Causes

Hyperpigmentation in dogs can be genetic or acquired. Here is a closer look at the causes of primary (genetic) and secondary (acquired) hyperpigmentation.

1. Aging

Mild hyperpigmentation can be the result of aging. In most cases, it is due to prolonged sun exposure. This is most likely seen in dogs with white or light-colored coats.

2. Obesity

Overweight and obese dogs are particularly prone to hyperpigmentation. You'll be more likely to notice darkened areas of skin, especially on the dog's back legs and the groin area.

Certain dog breeds are predisposed to weight gain. Pugs, Beagles, Cocker Spaniels, Red Fox Labrador Retrievers, Rottweilers, Cairn Terriers, etc., are predisposed to gaining weight.

Did you know? Obesity reduces the dog’s life expectancy and is a widespread problem. Namely, today, according to the Morris Animal Foundation, around 56 percent of dogs are either overweight or obese.

3. Hormonal Imbalances

Very high and low concentrations of certain hormones result in skin changes (in color, thickness, or consistency) and irritation, which causes itching, scratching and fur loss. Hormonal conditions affecting dogs that have been associated with the onset of secondary hyperpigmentation include the following:

Cushing’s Disease

This is an endocrine disease in which the dog’s adrenal glands produce too much cortisol (also known as the stress hormone). Signs of Cushing's disease include increased thirst, urination and appetite. However, skin symptoms are also widespread.

Hypothyroidism

An underactive thyroid gland results in low thyroid hormone levels. The lack of thyroid hormones slows down the dog’s metabolism resulting in weight gain and increased appetite. Other symptoms include skin problems and lethargy.

Diabetes Mellitus

Diabetes develops when the dog’s pancreas cannot produce enough insulin. The lack of insulin disrupts the normal metabolism of carbohydrates, causing weight loss. Diabetes also manifests with skin issues, increased thirst and urination.

4. Allergies

Allergies in dogs are associated with chronic itching. Chronic itching is the most common cause of secondary hyperpigmentation. In such cases, the darkening of the skin can result from constant licking or secondary skin infections.

Common allergies in dogs causing hyperpigmentation are:

Environmental Allergies

From grass, trees and pollen to dust, mold and mites, dogs have many potential allergens. In sensitive dogs, both direct contact and inhalation may result in allergy symptoms.

Flea Allergies

Some dogs are sensitive to flea saliva. The flea saliva is injected when the flea starts feeding. In allergic dogs, even one flea bite is enough to trigger a reaction.

Food Allergies

Sometimes the allergens are hidden in the dog's food or, better said, its protein source (beef, wheat, chicken, or dairy). Food allergies in dogs are challenging to diagnose and manage.

5. Skin Infections

Infections of the skin result in inflammation and irritation, which trigger increased deposition of melanin in the skin cells.

Other signs and symptoms of skin infections include constant itching, rashes, patchy hair loss, scabs and crusts.

Skin infection triggers in dogs include various microorganisms such as bacteria, fungi (ringworm and yeasts) and parasites (mange and mites).

6. A Side Effect of Drugs

Hyperpigmentation in dogs can be drug-induced (a side effect of long or repetitive use of certain medications). Potential culprits include:

Ketoconazole: A very commonly used antifungal medication available as a topical cream and oral tablets.

Mitotane: A chemotherapy medication used to treat Cushing’s disease and adrenal gland cancer.

Minocycline: A tetracycline antibiotic with a wide specter of efficacy (potent against gram-positive and gram-negative bacteria).

Cabergoline: A dopaminergic medication used in the treatment of mastitis, false pregnancy and problems with the estrus cycle.

7. A Sign of Tumors

The last cause of dog hyperpigmentation is skin tumors, primarily melanocytomas (benign) and melanomas (malignant). However, it can also be the result of basal cell tumors, epidermal and epithelial nevi, trichoblastomas and fibromas.

Melanomas and melanocytomas typically develop in older dogs—over nine years of age. They are also more common among certain breeds, such as Miniature and Standard Schnauzers, Irish Setters and Scottish Terriers.

This pigmented lesion on my dog's leg prompted surgical removal

Aleadry

What Are the Signs of Hyperpigmentation in Dogs?

Hyperpigmentation in dogs is a symptom on its own. However, it often co-exists with other skin issues. Here is what you can expect:

Discoloration

The darkened areas can be in any shade of brown (from light to very dark) or black. More often than not, such areas develop on the groins, armpits and back legs.

Red Circles

The edges of hyperpigmented areas often turn red as a result of secondary bacterial and fungal skin infections.

Alopecia

The darker skin areas are usually furless. When a dog presents with hair loss, it is medically referred to as alopecia. This hair loss usually develops after the area turns dark.

Lichenification

The dark skin areas or their immediate surrounding can become thick and with a pebble-like texture.

Depending on the exact underlying cause, the dog will show additional signs and symptoms that are not directly linked to the skin.

Hyperpigmentation vs. “Café au Lait” Spots

Hyperpigmentation should be differentiated from the so-called Café au Lait spots. Café au Lait spots are, in fact, birthmarks (like moles and freckles), which means spots featuring increased melanin production. They are purely cosmetic and do not require treatment.

Diagnosis and Treatment of Skin Darkening in Dogs

Hyperpigmentation in dogs is easy to spot. The real challenge is to determine the underlying cause of skin darkening.

To do this, the vet will start with a thorough physical examination. They will also take the dog’s history and talk to the owner to gather as much information as they can.

Based on the initial findings, the vet will order additional diagnostic tests such as blood analysis (blood cell counts and biochemistry profiles), skin biopsies, skin scrapings, food trials, etc.

What Is the Treatment for Hyperpigmentation in Dogs?

There is no universal treatment for hyperpigmentation in dogs; it depends on the underlying cause, and it can be fast and simple or challenging and long-lasting.

For example:

  • If caused by a flea allergy, eliminating the fleas will solve the problem.
  • If the trigger is melanocytoma, the dog will need a surgery.
  • If the skin darkening is due to hypothyroidism, the treatment will entail lifelong use of thyroid hormone supplements.
  • If the condition is drug-induced, discontinuing its use is likely to result in the normalization of the skin color.
Dark skin in dogs can be a sign of inflammation

Dimarik

As seen, hyperpigmentation in dogs is a darkening of the skin, which can be primary or secondary. In the first case, the issue is purely esthetic, and in the second, a sign of an underlying medical problem.

If your dog develops skin darkening, contact your trusted vet. Some causes are more benign than others, but they all require veterinary attention. The sooner you get help, the sooner your dog’s skin will return to its normal color.

Is Hyperpigmentation in Dogs Contagious?

No, being a symptom rather than a disease, hyperpigmentation in dogs cannot be contagious. However, some underlying causes of secondary hyperpigmentation, such as fleas, can be passed on to other pets (and humans).

Is Hyperpigmentation in Dogs Reversible?

Fortunately yes, secondary hyperpigmentation is reversible. Once the underlying cause is treated, the dog's darkened skin color is expected to return to normal. However, primary hyperpigmentation cannot be reversed.

Can I Treat My Dog's Dark Skin at Home?

No, you cannot treat a case of canine hyperpigmentation at home. Skin darkening in dogs can be a sign of a serious underlying condition. Therefore, when dealing with hyperpigmentation, your best course of action is to schedule a visit with your trusted vet.

References

  • Bajwa J. Cutaneous hyperpigmentation in dogs. Can Vet J. 2022 Jan;63(1):85-88. PMID: 34975173; PMCID: PMC8682925.
  • Goldschmidt MH. Pigmented lesions of the skin. Clin Dermatol. 1994 Oct-Dec;12

This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.

© 2023 Adrienne Farricelli CPDT-KA, Dip.CBST