A closer look: Skin Turning Black (Hyperpigmentation) in Dogs
Many dogs gradually develop darker areas of skin as they age. In many cases, this is purely a cosmetic concern and no action is necessary. Armpits, belly, flanks, and inner thighs are commonly affected areas.
Darkening of a dog’s skin is highly variable and may be:
- Progressive or static
- Localized to one specific area
- A solitary symptom
- Accompanied by other symptoms
- Primary (the genetic form)
- Secondary (the result of some other condition)
The amount of melanin can increase when the skin heals from an injury. Hyperpigmentation may go away once a minor injury heals, but when skin is chronically injured the change is often permanent.
Hyperpigmentation due to chronic inflammation is typically worse on the armpits and belly, itchy, and accompanied by secondary bacterial or fungal infections.
Some underlying conditions associated with hyperpigmentation are severe, so getting a veterinary opinion about any changes to the skin is beneficial.
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Dark patches develop when the amount of melanin in the skin increases.
Melanin increase occurs due to:
- Chronic irritation or inflammation
- Hormonal changes
- Prolonged sun exposure
Melanin levels also increase in association with acute conditions that damage the skin.
Dogs with hyperpigmentation from hormonal and genetic disorders are typically not itchy, at least at first.
Dogs with allergies, hypothyroidism, obesity, and mange are more likely to have areas of skin that become dark due to chronic irritation.
Hyperpigmentation occurs with chronically irritated skin, so it is common in dogs with underlying skin conditions that cause frequent licking, scratching, or skin that rubs like allergic dermatitis or obesity.
Some breeds have an inherited trait where the skin darkens as puppies mature, most commonly around one year of age. It most commonly affects the armpits and upper front legs of dachshunds.
While primary hyperpigmentation is an incurable inherited disorder that causes puppies to develop thick, dark skin as they mature, secondary hyperpigmentation always develops as a result of some other disease.
Hairless breeds may develop hyperpigmentation since they don’t have much fur to protect their skin.
A clearly defined, raised, dark spot with clearly defined margins is more likely to be a skin tumor.
Testing and diagnosis
If veterinary attention is warranted, evaluation of a dog whose skin is turning black starts with:
- Physical examination
- Skin scrape
- Bacterial and fungal culture
- Microscopic examination of cells and debris from the skin surface (cytology)
More complicated cases may undergo:
- Blood work
- Allergy testing
- Dietary trials
Treatment varies depending on the underlying condition and options include:
- Benign neglect
- Avoiding UV exposure
- Topical antimicrobials
- Oral antifungals and antibiotics
- Medications for hypothyroidism or Cushing syndrome
- External parasite control
- Allergy medication
Hyperpigmentation may fade over several months if the underlying cause is successfully treated.