In most cases, a dog’s scrotum turns black simply because of natural skin pigmentation, and it’s completely normal. Just like the skin on a dog’s nose, lips, or paw pads, scrotal skin darkens over time as melanin deposits increase with age. Many puppies start with pink or light-colored scrotal skin that gradually deepens to dark brown or black as they mature. This is one of the most common color changes dog owners notice and rarely signals a problem.
Normal Pigmentation Changes
Dogs’ skin pigments the same way human skin does, through melanin production. The scrotal skin is thin and often hairless, which makes color changes far more visible than on other parts of the body. A puppy might have light pink or spotted scrotal skin that transitions to gray, brown, or solid black over the first year or two of life. Some breeds are more prone to heavy pigmentation, particularly darker-coated dogs, but it happens across all breeds.
Pigmentation can also shift with the seasons. Sun exposure accelerates melanin production, so you might notice the skin getting darker in summer months. Hormonal changes, especially around sexual maturity (typically 6 to 12 months), often trigger a noticeable darkening. If the skin is smooth, not swollen, and your dog isn’t bothering with it, the black color is almost certainly just pigment.
Hyperpigmentation From Friction or Irritation
Sometimes scrotal skin darkens beyond normal pigmentation because of chronic low-grade irritation. Dogs that sit on rough surfaces, lick the area frequently, or deal with mild allergies can develop hyperpigmentation, where the skin thickens and darkens in response to repeated irritation. The skin may look velvety or slightly rougher than usual.
This type of darkening is common in dogs with environmental or food allergies. If your dog also has dark, thickened skin in the armpits, groin folds, or between the toes, allergies are a likely contributor. The black color itself isn’t dangerous, but it’s a sign that something is irritating the skin chronically. Addressing the underlying allergy, whether through diet changes or reducing environmental triggers, can slow further thickening.
Skin Infections and Dermatitis
Bacterial or yeast infections on the scrotal skin can cause darkening along with other noticeable symptoms. Yeast infections in particular tend to produce dark, thickened skin with a musty smell. You might also see redness at the edges of the darkened area, flaking, or greasy-looking skin. Dogs with yeast-related darkening often lick or scratch at the area persistently.
Contact dermatitis, caused by chemicals, cleaning products, or irritating ground surfaces, can also inflame scrotal skin and lead to color changes. In these cases the darkening usually comes with visible irritation: redness, small bumps, or peeling skin. If the black color appeared suddenly and comes with any of these signs, an infection or inflammatory reaction is more likely than normal pigmentation.
Testicular Tumors
Testicular tumors are worth knowing about, though they’re a less common explanation for color changes. The three main types in dogs are Sertoli cell tumors, Leydig cell tumors, and seminomas. They’re most common in intact (unneutered) dogs over 7 years old, and dogs with undescended testicles are at significantly higher risk.
Sertoli cell tumors can produce estrogen, which sometimes causes a set of changes called feminization syndrome: enlarged mammary tissue, symmetrical hair loss on the flanks, a change in how other dogs react to your dog, and skin changes including darkening. In one study of 11 dogs with Sertoli cell tumors, only one displayed feminization signs, so most testicular tumors don’t cause obvious hormonal symptoms. What you’re more likely to notice is one testicle becoming larger or firmer than the other, or a visible lump.
If your dog is intact, older, and you notice asymmetry between the testicles, firmness, or a lump alongside the color change, a veterinary exam is warranted. Most testicular tumors in dogs are benign and resolve completely with neutering.
Signs That Need Veterinary Attention
The black color alone, on smooth and comfortable-looking skin, is almost never a concern. But certain accompanying signs point to something that needs treatment:
- Pain or swelling: If the scrotum looks puffy, feels hot, or your dog reacts when you touch it, this can indicate infection, torsion, or inflammation of the testicles or surrounding structures.
- Open wounds or discharge: Any breaks in the scrotal skin, oozing, or crusting suggests injury or infection.
- Sudden color change: Gradual darkening over weeks or months is typically pigmentation. A rapid shift, especially to purple or deep red-black, can signal bruising or compromised blood flow.
- One testicle noticeably larger: Asymmetry in size or firmness warrants a check for tumors or fluid accumulation.
- Persistent licking: Occasional grooming is normal, but constant attention to the area suggests discomfort, itching, or pain.
Scrotal skin is thin and exposed, making it vulnerable to scrapes, insect bites, and sunburn that might not affect thicker, fur-covered skin elsewhere on the body. Light-skinned dogs with minimal scrotal hair can even develop sunburn that later heals with darker pigmentation. If you’re ever unsure whether a change is cosmetic or medical, a quick vet visit can rule out the more serious possibilities with a simple physical exam.