You are pretty familiar with your dog's stomach color after giving so many belly rubs, but now that you noticed your dog's stomach has turned dark, you are feeling concerned. In many dogs, the belly area is covered with skin that is of a pinkish or tan color. The color is easily visible here due to sparse hairs in the area, making the skin quite noticeable compared to other areas of the dog's body. A sudden color change is therefore something worthy of investigating, considering that in some cases, it can be indicative of serious trouble.
Possible Skin Problems
The medical term for darkening of a dog's skin is "hyperpigmentation. " The color change is typically caused by inflammatory cells known as macrophages which tend to release melanin, causing the dog's skin to turn black, explains veterinarian Dr. Peter.
But why does hyperpigmentation in dogs occur in the first place? It can happen as a result of several skin problems that trigger a chronic inflammatory response. Potential underlying skin problems may include allergies (especially if there is also itching), bacterial or yeast infections (the latter typically causing thickened, greasy skin with a sweet, yeasty odor), skin cancer or anything else that triggers inflammation.
It is therefore important to see the vet to get to the root of the problem. Your vet will examine this area, and may perform a skin scrape to find presence of yeast or bacteria or even a skin biopsy to rule out auto-immune diseases or neoplastic problems.
If allergies are suspected, (food allergies or allergies to something in the environment), your vet may suggest giving your dog an antihistamine and possibly, fish oil or he may suggest to do a food trial for 6 to 8 weeks. If a skin infection is suspected, the vet may prescribe special shampoos and/or a course of anti-fungal drugs or antibiotics.
Presence of Parasites
Another possibility for dark skin on a dog's belly is the presence of parasites, in particular, sarcoptes scabiei mites, which are known to cause in dogs sarcoptic mange. The mites cause dogs to be very itchy and the blackened skin may be sparse around the body.
Diagnosing sarcoptic mange in dogs though can be tricky. This is because the mites can be hard to find on the dog's skin during a skin scrape. Because of this, when vets suspect mange in dogs, they prefer to simply try to treat it and see how the dog responds.
A trial of Revolution therefore can provide an insight on whether or not the dog has mites.
"This is certainly less common, but the mites that cause this are difficult to find on scrapes, so negative scrapes do not rule out sarcoptic mange. In cases that I suspect it, I will treat for it even if I don't find the mites."~Dr. Coston, veterinarian
Problems with Hormones
Any time there are skin problems, hormonal issues in dogs should be considered a possibility, especially when the skin problems are associated with other symptoms such as increased drinking and increased urination.
Hormonal imbalances, also known as endocrine disorders, are known to cause hair loss in dogs and skin problems. Dogs in particular are more likely to develop two hormonal issues: hypothyroidism and hyperadrenocorticism, also known as Cushing's disease.
To test for these hormonal conditions your vet will need to run some blood tests.
To diagnose or rule out hypothyroidism, a T4 (thyroid hormone) and TSH (thyroid stimulating hormone) test is needed. To diagnose Cushings' instead, the vet may run a urine cortisol:creatinine ratio, a low dose dexamethasone suppression test, and possibly, an ultrasound.
Bleeding Under the Skin
Here is where things may get serious. In some cases, the dark skin is due to bleeding under the skin. In this case, the skin develops purple blotches that look like darkened, bruised areas. Such bruising (medical term is ecchymosis) is considered a medical emergency because it can be a sign of a blood clotting disorder.
Blood clotting problems may be triggered by ingestion of rat poison or some other blood clotting disorder affecting dogs such as thrombocytopenia (causing low platelet counts). Other signs of trouble indicative of a blood clotting disorder include pale gums, lethargy, hemoabdomen, petechiae (pinpoint, round bleeding spots on the skin), cold extremities.
As seen, the possible causes of a darkened belly in dogs can be several. On a lighter note, in some cases, the darkening of the dog's skin on the belly may be just a normal skin color change as seen when a puppy grows older or as it happens during the spring/summer in dogs who like to lie out in the sun belly-up, explains Dr. Shannan, an associate veterinarian.
In some other cases, the bruising can be a result of trauma, such as from a kick or fall. Because of the several possibilities and the risks for serious underlying disorders, it's best to see the vet for proper diagnosis and treatment.
"Discoloration of purple can be bleeding in the skin from coagulation disorder or low platelets (thrombocytopenia). The best thing to do is have a vet take a look at this discoloration. The two latter conditions if untreated can be fatal."~Dr. Peter, veterinarian