Some dogs develop patches of skin that turn brown or black and feel thick and rough, often in the armpits, the groin or on the legs. Vets call the darkening hyperpigmentation and the thickening lichenification. The older name acanthosis nigricans is also used for this picture.
Dark, thick skin is usually a response to something else going on in or on the skin. University of Minnesota dermatology teaching material lists darkening and thickening as classic signs of long-lasting inflammation. [2] In other words, the dark skin is a clue, and the real job is finding what caused it.
What it looks like
Affected skin turns light brown to black and becomes thicker and rougher, a bit like leather. Hair over it is often thin or missing. [1][2]
Yeast overgrowth (Malassezia) tends to show up in the folds and warm areas: the lip folds, the underside of the neck, the armpits, the groin, between the toes and around the vulva. Early on the skin is red, sometimes with brownish staining of the hair and scale; in long-standing cases it becomes thick and dark. [1][2] Red edges, scale, crusts or pimples on or around a dark patch can point to a yeast or bacterial infection on top of the original problem. [1][3] Itching varies from dog to dog. [3]
Common causes
Darkening of the skin can follow many different problems. The ones your vet will usually think about first are: [1][2][3][4][5]
- Allergies, such as atopic dermatitis, food allergy or flea allergy, where months of scratching and licking leave the skin thick and dark
- Yeast (Malassezia) overgrowth, which is common in allergic dogs and in chronically thickened skin
- Bacterial skin infection (pyoderma), which is usually secondary to another skin disease
- Hormone disorders, such as an underactive thyroid or Cushing’s disease
- Skin parasites, such as mites, that cause itching and inflammation
Because of this, darkening that keeps spreading or comes with other skin changes is worth a vet visit rather than a wait-and-see approach.
Links to itch, infection and hormones
In allergic dogs, chronic itch leads to hair loss from scratching, and the skin gradually darkens and thickens. Secondary bacterial and yeast infections are very common in these dogs and can make the itch worse. [2][3]
Hormone problems can also be involved. In dogs with an underactive thyroid, typical skin signs are hair loss on both sides of the trunk with darkened skin, usually without itching, and the tail can lose its hair as well. [4] In Cushing’s disease (overactive adrenal glands), darkened skin is common, along with thin skin, hair loss, a pot belly and blackheads on the belly. [5]
Related guides: why is my dog so itchy?, seasonal allergies in dogs, pyoderma in dogs and hair loss in dogs.
What your vet will check
The work-up starts with a careful history and physical examination to find the underlying cause. Depending on the dog, tests may include: [1][2][3][4][5]
- Skin scrapings to look for mites and other parasites
- Cytology (sticky tape or slide samples looked at under the microscope) to look for bacteria and yeast
- Blood tests for thyroid and adrenal function if a hormone problem is suspected
- An allergy work-up, which means ruling out other itchy skin diseases such as food allergy, flea allergy and mange
Infections found on the skin are usually treated alongside the search for the main cause, because they add to the itch and inflammation. [3]
How it is treated
Treatment is aimed at the cause, not at the color. Finding and managing the underlying disease is what helps the skin settle and keeps yeast and bacterial infections from coming back. [1][3] Your vet may combine this with treatment for any secondary infection, including medicated baths, and will tailor the plan to your dog.
Be patient. Thickened, darkened skin has usually built up over a long time, so ask your vet what change to expect and when to come back for a recheck.
When to see your vet
Book a visit if your dog has:
- Skin that is turning dark, thick or rough
- Dark patches with red edges, discharge or hair loss
- Itching, licking or chewing at the area
- Darkening skin along with other changes, such as hair loss elsewhere on the body
FAQ
Is it normal for a dog’s belly skin to be dark?
Some dogs simply have dark skin. Skin that is turning dark, thick, rough or hairless is different and is worth a vet check, because it is often a sign of long-lasting inflammation from allergy, infection or a hormone problem. [2][4][5]
Will the dark skin go away?
It often improves once the underlying cause is found and managed and any infection is under control, but the change is gradual. Your vet can tell you what to expect for your dog. [1][3]
Is it itchy?
It depends on the cause. Allergies and yeast or bacterial infections are usually itchy, while hormone-related darkening often is not, unless an infection develops on top. [2][3][4]
The bottom line
Dark, thickened skin on a dog is a sign, not a diagnosis. It usually points to an underlying problem, such as allergy, infection, parasites or a hormone disorder, and it is that cause your vet will look for and treat. [1][2][3][4][5]
This article is for general information and is not a substitute for veterinary advice. If your dog’s skin is changing color or texture, please see your veterinarian.
Sources
- Torres SMF, et al. 4.3 Malassezia Dermatitis: Small Animals. Small and Large Animal Dermatology Handbook, Vol. 1. University of Minnesota Libraries Publishing, 2025 (CC BY 4.0). https://open.lib.umn.edu/animaldermatology/chapter/malassezia-dermatitis-small-animals/
- Torres SMF, et al. 2.1 Atopic Dermatitis: Dogs. Small and Large Animal Dermatology Handbook, Vol. 1. University of Minnesota Libraries Publishing, 2025 (CC BY 4.0). https://open.lib.umn.edu/animaldermatology/chapter/atopic-dermatitis-dogs/
- Torres SMF, et al. 1.1 Canine Pyodermas. Small and Large Animal Dermatology Handbook, Vol. 1. University of Minnesota Libraries Publishing, 2025 (CC BY 4.0). https://open.lib.umn.edu/animaldermatology/chapter/canine-pyodermas/
- Torres SMF, et al. 1.5 Hypothyroidism: Canine. Small and Large Animal Dermatology Handbook, Vol. 2. University of Minnesota Libraries Publishing, 2025 (CC BY 4.0). https://open.lib.umn.edu/animaldermatology2/chapter/hypothyroidism-canine/
- Torres SMF, et al. 1.2 Hyperadrenocorticism: Canine. Small and Large Animal Dermatology Handbook, Vol. 2. University of Minnesota Libraries Publishing, 2025 (CC BY 4.0). https://open.lib.umn.edu/animaldermatology2/chapter/hyperadrenocorticism-canine/