Dogs get bald spots for a wide range of reasons, from flea bites and skin infections to hormonal imbalances and stress. Some causes are minor and resolve on their own, while others signal an underlying condition that needs treatment. The location, shape, and pattern of hair loss often reveal a lot about what’s going on.
Parasites: Fleas and Mange Mites
Parasites are one of the most common reasons dogs lose patches of fur. Flea allergy dermatitis is especially widespread. Dogs with this condition are highly sensitive to flea saliva, so even a single bite can trigger intense itching, scratching, and hair loss. The bald spots typically show up around the tail base, belly, and inner thighs, often with red bumps and scabbing from constant scratching.
Mange mites cause a different pattern. Sarcoptic mange (canine scabies) is highly contagious between dogs and produces thick, yellow crusts along with hair loss that usually starts on the belly, chest, ears, elbows, and hocks. Left untreated, it spreads across the body. The itching is relentless. Demodectic mange, on the other hand, isn’t contagious. Puppies pick up the mites from their mother during nursing in the first 72 hours of life, and most dogs carry them without problems. When the immune system falters, the mites overpopulate, causing one to five small, well-defined bald patches, usually around the lips, eyes, and front legs. In severe cases, the hair loss becomes widespread and complicated by secondary bacterial infections.
Fungal and Bacterial Skin Infections
Ringworm, despite the name, is a fungal infection. Infected dogs develop bald, scaly patches with broken hairs, most commonly on the face, ear tips, tail, and feet. Dogs may also develop acne-like bumps. Ringworm is contagious to other animals and to people, so prompt treatment matters.
Bacterial skin infections (pyoderma) look somewhat different. The hallmark is excessive scaling, often with scales pierced by hairs. In short-haired breeds, the infection creates multiple raised welts that resemble hives because inflammation around the follicles pushes hairs upright. Those hairs pull out easily. Deeper bacterial infections cause pain, crusting, odor, and discharge of blood or pus. Pyoderma is frequently a secondary problem, meaning something else triggered it: allergies, hormonal disorders, or parasites weakened the skin’s defenses first.
Hormonal Imbalances
When hair loss appears symmetrically on both sides of the body without much itching, a hormonal condition is often the cause. Two of the most common are hypothyroidism and Cushing’s syndrome.
Dogs with Cushing’s syndrome produce too much of the stress hormone cortisol. Along with symmetrical hair loss, you’ll typically notice a pot belly, thinning skin, and increased thirst and urination. The skin can become so thin it tears easily, and in some cases calcium deposits form under the skin surface. Cushing’s is most common in middle-aged and older dogs.
Hypothyroidism, where the thyroid gland doesn’t produce enough hormone, slows hair follicle growth directly. Dogs with this condition often have a dull, thinning coat, gain weight without eating more, and seem sluggish. Both conditions require blood tests to diagnose and ongoing treatment to manage, but hair typically regrows once hormone levels stabilize.
Allergies Beyond Fleas
Environmental allergens like pollen, dust mites, and mold can trigger chronic itching that leads to hair loss. So can food sensitivities. The pattern depends on where the dog scratches, licks, or chews most. Allergic dogs often lose hair on their paws, belly, armpits, and ears. The skin underneath may look red, thickened, or darkened from chronic irritation. Allergy testing is usually done after other causes like parasites and infections have been ruled out, because the symptoms overlap so heavily.
Genetic and Breed-Related Hair Loss
Some dogs are genetically predisposed to hair loss. Color dilution alopecia affects dogs with “dilute” coat colors, particularly blue, fawn, or bluish-gray fur. These dogs carry a recessive gene that causes hair follicles to essentially self-destruct, making it impossible to grow new hair in affected areas. The condition has been commonly described in blue Dobermans but occurs in dozens of breeds, including Dachshunds, Great Danes, Italian Greyhounds, Yorkshire Terriers, Labrador Retrievers, and Chihuahuas. Signs include patchy thinning, flaky skin, and sometimes itchiness, typically developing in the first one to three years of life.
Seasonal flank alopecia is another pattern with a likely genetic component. Dogs develop well-defined bald patches on their flanks, most commonly between November and April when daylight hours are shortest. Shorter days appear to trigger a shutdown of hair follicle activity. The hair often regrows on its own as days lengthen, though it may come back a different texture or color. Some dogs experience it once and never again; others deal with it every winter.
Stress, Boredom, and Compulsive Licking
Dogs that lick or chew the same spot repeatedly can create a firm, hairless, thickened patch called an acral lick granuloma. These lesions are typically oval or circular, most often appearing on the front of the wrist or top of the paw. The surrounding fur turns brown from saliva staining, which is a telltale sign the dog has been focused on that area.
An estimated 70% of dogs with this condition have an underlying anxiety-related issue, whether that’s separation anxiety, noise phobia, or simple boredom from lack of social interaction and mental stimulation. Dogs that live entirely outdoors, spend long hours crated, or are kept chained are especially prone. The licking triggers the release of endorphins, which both relieve pain and create a feedback loop that essentially makes the behavior addictive. Over time, the lesion becomes chronic: the skin thickens with scar tissue, the surface erodes or ulcerates, and breaking the cycle gets harder. That said, veterinary dermatologists now recognize that many cases also have an underlying physical trigger, like a joint ache, nerve irritation, or infection, that started the licking before anxiety sustained it.
Other Physical Causes
Not every bald spot has a complex explanation. Friction from a poorly fitted collar or harness can rub fur away. Burns, wounds, or surgical sites may leave permanent bare patches if the hair follicles were destroyed. Temporary hair loss also occurs during pregnancy, lactation, or in the weeks following a severe illness or high fever, as the body diverts resources away from hair growth. Nutritional deficiencies, particularly inadequate protein intake, can slow follicle activity and thin the coat overall.
How Vets Identify the Cause
Because so many conditions look similar on the surface, vets follow a layered diagnostic approach. The first step is usually a skin scraping, where a blade gently collects cells and debris from the affected area to check under a microscope for mites and other organisms. Cytology, examining a sample of surface cells, helps identify bacterial or yeast infections. If ringworm is suspected, a fungal culture of hairs and skin scrapings from the bald spot is the most accurate test, though some fungi glow under an ultraviolet lamp for a quicker preliminary check.
When infections and parasites are ruled out, blood work comes next to check thyroid function and cortisol levels. Allergy testing, either through skin injections or blood panels, is typically reserved for cases where everything else has been excluded. For unusual or persistent hair loss, a skin biopsy provides the most detailed information. A small full-thickness sample of skin is examined under a microscope to evaluate the hair follicles themselves, which is particularly useful for diagnosing autoimmune skin diseases, genetic follicle disorders, and cancer.
The location, symmetry, and whether the dog is itchy narrow things down considerably before any test is run. Symmetrical, non-itchy hair loss points toward hormones or genetics. Patchy, itchy bald spots suggest infections, parasites, or allergies. A single thickened lesion on a leg raises suspicion for compulsive licking. Bringing a clear photo and noting when the hair loss started, whether it’s spreading, and any other changes in your dog’s behavior or appetite gives the vet a significant head start.