Hair loss in dogs has dozens of possible causes, ranging from parasites and allergies to hormonal imbalances and genetics. Some forms are temporary and resolve on their own, while others signal an underlying condition that needs veterinary attention. The pattern, location, and speed of hair loss all offer clues about what’s driving it.
Parasites: Mange Mites and Fleas
Two types of mites cause the skin disease known as mange, and each produces a distinct pattern of hair loss. Sarcoptic mange (scabies) starts as crusty, yellow patches on the belly, chest, ears, elbows, and hocks. Dogs itch intensely, and without treatment the hair loss spreads across the body. The skin thickens and forms folds, and dogs can become emaciated. In well-groomed dogs, scabies sometimes hides in plain sight because regular bathing removes the telltale crusts and scales, making the mites harder to find on skin scrapings even though the dog is clearly itchy.
Demodectic mange looks different. The localized form typically shows up as one to five small, well-defined bald spots, often around the lips, eyes, and front legs. The skin in those patches may be red and scaly but not necessarily itchy. Generalized demodicosis is more serious, with widespread redness, oily skin, darkened patches, and crusty sores complicated by secondary bacterial infections. It can appear in puppies (juvenile-onset) or in adult dogs, where it often points to a weakened immune system.
Fleas cause hair loss through an allergic reaction to their saliva, not just from scratching. In flea allergy dermatitis, the classic pattern is thinning and bald patches from the middle of the back to the base of the tail and down the rear legs. Veterinarians sometimes call this the “flea triangle.” A dog with a true flea allergy can lose significant hair from just a handful of bites.
Hormonal Imbalances
When hair loss appears symmetrically on both sides of the body, especially along the trunk and tail, a hormonal problem is one of the first things to investigate. The two most common endocrine causes are an underactive thyroid and overactive adrenal glands (Cushing’s disease).
In hypothyroid dogs, the hair doesn’t fall out from excessive shedding the way most owners assume. Instead, hairs get stuck in a resting phase and simply stop growing. The coat thins gradually, typically along the back and tail, while the head and lower legs keep a normal coat. Because thyroid hormone plays a role in skin oil production and immune defenses, hypothyroid dogs also tend to develop chronic ear infections and dull, greasy skin.
Cushing’s disease produces a similar symmetrical pattern, but the hair loss tends to be more dramatic and complete on the trunk. The excess cortisol flooding the body also causes increased thirst, a pot-bellied appearance, and thin, fragile skin. About 90% of dogs with Cushing’s disease show elevated cholesterol on bloodwork due to the cortisol-driven changes in fat metabolism.
Allergies and Skin Infections
Beyond flea allergies, dogs can react to environmental triggers like pollen, dust mites, and mold, or to ingredients in their food. Environmental allergies (atopic dermatitis) usually cause itching on the face, paws, ears, and belly. Dogs scratch, chew, and lick those areas until the hair thins or disappears entirely. Food allergies can look similar, and the only reliable way to tell the two apart is a strict elimination diet lasting several weeks.
Ringworm, despite its name, is a fungal infection rather than a worm. It typically creates patchy areas of hair loss with a crusty or scaly surface. Some dogs show grey, flaky patches; others develop red lesions. The bald spots most commonly appear on the paws, legs, head, and ears, though they can show up anywhere. Ringworm is contagious to other animals and to people, which makes early identification important. Diagnosis is more reliable with a fungal culture or PCR test than with a skin biopsy alone, since cultures are more sensitive at confirming the specific fungus involved.
Stress and Behavioral Causes
Dogs can lick themselves bald. Acral lick dermatitis is a condition where a dog obsessively licks one spot, usually on a lower leg, until it becomes a raised, thickened, ulcerated plaque. The behavior can start from boredom, anxiety, or a compulsive disorder, but it quickly becomes self-reinforcing. The licking damages the skin, which triggers itching and secondary infections, which drives more licking. Breaking that cycle requires identifying and treating whatever started it, clearing any infection, and often addressing the behavioral component with environmental changes or medication.
Genetic and Breed-Related Hair Loss
Some dogs are genetically programmed to lose their hair. Color dilution alopecia is one of the more common inherited forms, affecting dogs with “dilute” coat colors, particularly blue (a diluted black) and fawn (a diluted brown or red). The condition doesn’t appear at birth. Puppies are born with a normal-looking coat, but hair gradually thins and breaks as they mature. Among blue and fawn Doberman Pinschers, the incidence is striking: roughly 58% of blue Dobermans and nearly 90% of fawn Dobermans develop it. Yorkshire Terriers, Dachshunds, Schnauzers, Italian Greyhounds, Chihuahuas, Whippets, Standard Poodles, and several other breeds are also affected.
A related condition called black hair follicular dysplasia targets only the black-pigmented areas of a dog’s coat. Most researchers now believe both conditions are different expressions of the same underlying genetic defect. Other forms of follicular dysplasia show up early in life in predisposed breeds, with hair loss that looks like a disruption in the normal hair growth cycle. These conditions are managed rather than cured.
Nutritional Deficiencies
Zinc plays a direct role in hair growth. It’s required for the enzymes that build and maintain hair follicles, and when levels drop, hair growth slows and coat quality visibly declines. Studies measuring zinc’s effect on dogs have tracked hair growth rate, coat brightness, softness, greasiness, and scaling, and all improve when zinc intake is adequate. The catch is that zinc absorption can be blocked by other dietary components. Phytates (found in grains and plant-based ingredients) bind to zinc and form insoluble complexes that pass through the gut unabsorbed. High levels of calcium, copper, or iron in the diet can also interfere with zinc uptake.
Some breeds, particularly Siberian Huskies and Alaskan Malamutes, are prone to zinc-responsive dermatosis, where they develop crusty, scaly skin and hair loss around the face and feet even on diets that contain normal zinc levels. These dogs need supplemental zinc to overcome a genetic limitation in absorption.
How Veterinarians Identify the Cause
The diagnostic process usually starts with the least invasive tests. A deep skin scraping can reveal mites. A fungal culture or PCR test checks for ringworm. Bloodwork can flag thyroid or adrenal problems. If those come back normal, the next step is often a skin biopsy.
For hair loss cases, veterinary pathologists recommend collecting at least three biopsy samples: two from the most affected area and one from a patch of normal skin for comparison. The biopsy site shouldn’t be prepped the way a surgical site would be, because scrubbing can remove the crusts and surface changes that hold diagnostic clues. Hair at the site is trimmed with scissors rather than shaved, and surface flaking is left intact.
Timing matters too. If a dog is on corticosteroids, oral forms ideally need to be stopped two to three weeks before the biopsy, and long-acting injectable steroids six to eight weeks before. Secondary bacterial infections should be cleared up first when possible, because they can mask the underlying disease pattern under the microscope.
What to Expect With Hair Regrowth
Once the underlying cause is addressed, regrowth timelines vary widely. For autoimmune-related hair loss like alopecia areata, about 60% of dogs regrow hair spontaneously within months of diagnosis. Resistant cases often respond to immune-modulating medication. Hormonal conditions like hypothyroidism typically show visible coat improvement within a few months of starting thyroid supplementation, though full regrowth can take longer. Parasitic causes tend to resolve relatively quickly once the mites or fleas are eliminated. Genetic conditions like color dilution alopecia have no cure, but managing secondary skin infections and supporting coat health can minimize further loss.