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Ask the Vet: What Causes Black Skin on a Dog's Belly?

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Causes of Black Skin on a Dog's Belly

Black skin on a dog's belly is certainly something that may concern dog owners. When a dog’s cute, pink and soft belly develops black spots or turns completely black (or even black and scaly) it is only natural for dog parents to panic. But is there really a reason to panic? Well…that depends on the case. Some skin conditions trigger loss of skin pigment while others cause increased pigmentation.

What causes black skin on a dog's belly?

What causes black skin on a dog's belly?

Why is The Skin on My Dog's Belly Turning Dark?

Many causes of pigment changes are of no medical consequence but some are good clues to the presence of other conditions. Although most dog parents believe that the skin darkening occurred suddenly, hyperpigmentation develops over time and is usually due to continual skin trauma. It is not uncommon for the trauma to have been present months before the darkening develops.

It should also be mentioned that even if the underlying cause is determined and corresponding treatment is completed, the skin may never return to its normal light color. Nevertheless, treating the underlying cause is of imperative importance for the dog’s health and comfort.

The term hyperpigmentation indicates skin darkening or increased concentration of pigment on a certain skin area. It goes without saying that hyperpigmentation is more dramatic and intense in dogs with lighter skin and fur.

Breeds most susceptible to hyperpigmentation include:

  • Beagles
  • Boston Terriers
  • Boxers
  • Chinese Shar Peis
  • Cocker Spaniels
  • Dachshunds
  • Doberman Pinscher
  • Great Danes
  • Irish Setters
  • Old English Sheepdog
  • Scottish Terrier
  • Weimaraner
  • West Highland White Terrier

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What Causes Black Skin on a Dog's Belly?

As previously stated hyperpigmentation can be triggered by a plethora of conditions. Some of those conditions are normal and some are due to underlying pathological issues. Namely, exposure to sunlight and almost any form of chronic skin irritation or inflammation may trigger changes of the skin that eventually lead to hyperpigmentation. Here is a detailed list of the most common causes of hyperpigmentation in dogs.

Old Age 

Some dogs develop dark skin patches as they get older. The darkened patches are neither itchy nor scaly. Although changed color, the skin is not thickened at all. Dark spots on the belly due to old age do not have on odour and are not accompanied by hair loss.

Allergies 

If you or I suffer from an allergy, we are likely to have itchy eyes and a runny nose or worse, lung congestion. When dogs have allergic reactions they develop itchy skin. The skin may become so itchy that dogs damage themselves by increased scratching, licking and chewing and may develop a whole range of secondary complications (bacterial or fungal infections).

Allergies are diagnosed by elimination diet trials, intradermal skin tests and ELISA tests. Allergies can be addressed with corticosteroids and antihistamines, environmental control or desensitizing vaccines.

Flea Allergy Dermatitis

This type of dermatitis is triggered by a reaction to substances in flea saliva that are left in the dog’s skin after a flea has a blood meal. Flea allergy dermatitis initially causes immediate itching and scratching followed by red, raised pimples. Eventually, the skin becomes thickened and darker, and may also be dry, stinky and scaly.

ELISA blood test and intradermal skin test are used to confirm the diagnosis. The treatment involves eliminating the fleas and preventing their return.

Skin Infections 

Skin infections are a common cause of chronic irritation and consequently hyperpigmentation. They can develop on their own or secondary to allergies or other conditions that cause itching and scratching. Based on what causes them there are several types of skin infections:

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Bacterial and yeast infections – these are the most common types. Malassezia dermatitis is a type of yeast infection that causes itchy redness of the skin followed by crusting and darkening.

Bacterial and yeast infections are treated with antibiotics or antifungal medications accordingly. The treatment can be oral, topical or combined.

Mange (demodex and sarcoptic) – these mites cause intense itching and scratching followed by darkening of the skin. Once the mites are eliminated the discoloration usually resolves. However, in more severe cases the skin darkening is permanent.

Ringworm (dermatophytosis) – this fungal infection causes skin infection that manifests with circular loss of hair, excessive licking and scratching of the affected areas and ultimately skin darkening.

The treatment includes topical and oral antifungal medications.

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 Hormonal Imbalances 

Overactive adrenal gland – also known as Cushing’s disease is a disorder caused by tumors in the adrenal gland or excessive medical use of corticosteroids. Affected dogs have the following symptoms – excessive drinking and urinating, increased appetite, distended abdomen and hair loss followed by skin darkening.

A definitive diagnosis is made by monitoring the cortisol response to stimulating/suppressing drugs. The treatment includes drugs that suppress the gland’s activity.

Underactive thyroid gland – hypothyroidism is usually an immune-mediated condition. Cocker Spaniels, Doberman Pinschers and Golden Retrievers are particularly prone to thyroid disorders. Dogs with hypothyroidism have a deficiency of thyroid hormone and as a result they become lethargic, overweight and less exercise tolerant. They are also more prone to skin infections followed by hyperpigmentation.

The diagnosis is based on measuring the levels of the hormone thyroxine in the blood. The treatment includes administration of a synthetic thyroid hormone (L-thyroxine).

 Excessive Licking

Some dogs tend to incessantly lick certain areas of the body including their bellies. The constant licking as a combination of mechanical and chemical irritation damages the fur and skin. Over time, the fur hair falls out and the skin first reddens and then darkens. More often than not, the excessive licking is due to anxiety or boredom.

The diagnosis is based on elimination of other possible causes. The treatment includes addressing the secondary complications that may arise from the licking and discouraging further licking.

Acanthosis Nigricans in Dachshunds

The Dachshund uniquely suffers from a hyperpigmentation condition called acanthosis nigricans. Although the exact cause is poorly understood, it is postulated that the skin darkens as a consequence to chronic inflammation.

Diagnosis is by signs, breed and elimination of other causes. Topical corticosteroid cream is sometimes used to relieve the inflammation.

About the Author

ivana crnec

Dr. Ivana Crnec is a graduate of the University Sv. Kliment Ohridski’s Faculty of Veterinary Medicine in Bitola, Republic of Macedonia. She currently practices as a veterinarian in Bitola and is completing her postgraduate studies in the Pathology of Domestic Carnivores at the Faculty of Veterinary Medicine in Zagreb, Croatia.

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