Symptoms & Diagnosis

Why Is My Dog Losing Hair? Causes, Diagnosis, and Treatment

By Emiel Maddens · Reviewed in consultation with licensed veterinary professionals · Updated April 2026 · 10 min read

Dog with thinning coat, hair loss can signal allergies or hormonal disease

Key Takeaways

Hair loss (alopecia) in dogs is a symptom, not a diagnosis. The pattern, location, and speed of hair loss are the most important clues to the underlying cause.
Allergic skin disease is the most common reason dogs lose hair, because chronic scratching and licking damages hair follicles.
Symmetrical hair loss without itching is a red flag for hormonal disease, most commonly hypothyroidism or Cushing's disease.
Patchy hair loss in circular patterns may indicate a fungal infection (ringworm) or bacterial infection, both of which are treatable.
A thorough diagnostic workup, including skin scraping, fungal culture, bloodwork, and possibly biopsy, is often needed to identify the root cause.

Finding clumps of fur on the couch, bald patches appearing on your dog's flanks, or watching the coat thin out week by week is understandably alarming. Hair loss in dogs, called alopecia in veterinary medicine, is one of the most common reasons for dermatology referrals, and the list of possible causes is long. The good news is that the pattern of hair loss itself tells a story, and an experienced veterinarian can often narrow the list significantly based on where the hair is falling out and whether the dog is itchy.

This guide walks through the most common causes of canine hair loss organized by what the pattern looks like, explains the diagnostic steps, and covers the treatment options for each. Whether the hair loss started suddenly or has been progressing slowly for months, the approach is the same: identify the pattern, run the right tests, and treat the underlying cause rather than the symptom.

The Most Common Causes of Hair Loss in Dogs

Veterinary dermatologists group canine alopecia into two broad categories: hair loss caused by the dog damaging their own coat (pruritic alopecia, from scratching and licking) and hair loss where the follicles stop producing hair on their own (non-pruritic alopecia). This distinction is the first and most important diagnostic step.

1. Allergic Skin Disease (Self-Inflicted Hair Loss)

The most common cause of hair loss in dogs is not a hair problem at all. It is a skin problem. Dogs with environmental allergies (atopic dermatitis), food allergies, or flea allergy dermatitis scratch, lick, chew, and rub their skin, which breaks hair shafts and damages follicles. The hair loss follows the itch: paws, face, ears, belly, and armpits are the classic locations. If the dog is visibly itchy and the hair loss is in areas they can reach with their mouth or paws, allergies are the most likely explanation.

2. Hypothyroidism

Hypothyroidism is the most common hormonal cause of hair loss in dogs. The thyroid gland produces insufficient thyroid hormone, which slows metabolism and disrupts the hair growth cycle. The hallmark pattern is bilateral, symmetrical hair loss on the trunk (flanks, back, tail base) that spares the head and legs. The skin underneath is often thickened, dry, and may be hyperpigmented. Affected dogs are typically not itchy unless a secondary infection develops. They may also show weight gain, lethargy, cold intolerance, and a slowed heart rate. Diagnosis is confirmed with blood tests (total T4, free T4, TSH), and treatment with daily levothyroxine supplementation usually produces visible coat regrowth within 2 to 3 months.

3. Cushing's Disease (Hyperadrenocorticism)

Cushing's disease causes the adrenal glands to produce excess cortisol, which thins the skin, weakens hair follicles, and suppresses the immune system. Hair loss is typically symmetrical, widespread, and non-pruritic. The skin becomes thin, bruises easily, and may develop comedones (blackheads) or calcinosis cutis (hard, white calcium deposits). Other signs include increased thirst and urination, a pot-bellied appearance, panting, and muscle weakness. Diagnosis requires specific endocrine testing (ACTH stimulation or low-dose dexamethasone suppression test).

4. Demodex Mange (Demodicosis)

Demodex mites live in hair follicles and are normally present in small numbers on all dogs. When the immune system is compromised, the mite population can explode and cause patchy to generalized hair loss. Localized demodicosis (a few small patches) is common in puppies and often self-resolves. Generalized demodicosis (widespread hair loss with secondary infection) requires treatment with isoxazoline-class parasiticides. The hair loss is typically non-pruritic unless secondary bacterial infection develops.

5. Ringworm (Dermatophytosis)

Despite its name, ringworm is a fungal infection, not a worm. It causes circular patches of hair loss with a scaly, crusty border. The patches may or may not be itchy. Ringworm is contagious to other animals and to humans, making accurate diagnosis important. Diagnosis is confirmed with fungal culture or PCR testing. Treatment involves both topical antifungals and systemic antifungal medication for 6 to 8 weeks minimum.

6. Bacterial Skin Infection (Pyoderma)

Deep bacterial skin infections can destroy hair follicles and cause permanent hair loss in the affected areas. Superficial pyoderma more commonly causes temporary hair loss that regrows after the infection resolves. Bacterial folliculitis, infection of the hair follicle itself, is a common secondary problem that rides on top of allergies or other primary skin diseases.

7. Color Dilution Alopecia

This genetic condition affects dogs with dilute coat colors, particularly blue (dilute black) and fawn (dilute red) coats. The dilution gene causes structural defects in the hair shaft that lead to breakage and progressive hair loss, typically beginning between 6 months and 3 years of age. Dobermans, Italian Greyhounds, Whippets, and other breeds carrying the dilution gene are most commonly affected. There is no cure, but the condition is cosmetic.

8. Seasonal Flank Alopecia

Some dogs develop predictable, bilateral hair loss on the flanks during fall and winter that spontaneously regrows in spring. The exact mechanism is thought to be related to changes in melatonin levels with decreasing daylight hours. Boxers, English Bulldogs, Airedales, and Schnauzers are most commonly affected. The condition is purely cosmetic and requires no treatment.

Dog being examined by veterinarian for hair loss and skin condition

Which Breeds Are Most Affected?

Certain breeds are predisposed to specific types of hair loss:

Labrador Retriever: High allergy rates make self-inflicted hair loss from scratching and licking extremely common.
Golden Retriever: Prone to allergies, hypothyroidism, and hot spots, all of which cause hair loss.
German Shepherd: Predisposed to allergic skin disease and deep pyoderma that can cause permanent follicular damage.
Doberman: The breed most commonly affected by color dilution alopecia, plus high rates of hypothyroidism.
English Bulldog: Widespread allergic disease and secondary infections frequently cause coat thinning and bald patches.
Boxer: Prone to seasonal flank alopecia, Demodex, hypothyroidism, and allergic hair loss.
Dachshund: Predisposed to pattern alopecia, acanthosis nigricans, and Cushing's disease-related hair loss.
Shar-Pei: High rates of Demodex, allergies, and hypothyroidism all contribute to hair loss in this breed.
Poodle: Prone to sebaceous adenitis, a condition that destroys the oil glands in hair follicles and causes progressive hair loss.
Yorkshire Terrier: Susceptible to alopecia areata and color dilution alopecia in blue-coated individuals.

How to Assess Your Dog's Hair Loss at Home

Before your vet visit, documenting these details will help with diagnosis:

Map the Pattern

Where exactly is the hair falling out? Symmetrical loss on both flanks suggests hormonal disease. Patchy, circular lesions suggest ringworm or bacterial infection. Hair loss concentrated on paws, face, belly, and ears suggests allergies. Take photos from multiple angles with good lighting.

Assess Itchiness

Is the dog scratching, licking, or chewing the areas where hair is falling out? Itchy hair loss points toward allergies, infections, or parasites. Non-itchy hair loss points toward hormonal disease, genetic conditions, or immune-mediated causes.

Check the Skin Underneath

Part the remaining hair and examine the skin in the bald areas. Red, inflamed skin suggests infection or allergy. Dry, thickened, or darkened skin suggests chronic inflammation or hormonal disease. Scaly, crusty borders around circular patches suggest ringworm.

Note the Timeline

Did the hair loss start suddenly or gradually? Sudden onset suggests an acute cause like an infection, mite infestation, or drug reaction. Gradual progression over months is more consistent with hormonal disease, allergies, or genetic conditions.

Check for Other Symptoms

Hair loss combined with increased thirst and urination, weight gain, lethargy, or a pot-bellied appearance strongly suggests an endocrine (hormonal) disorder. Hair loss with intense itching, ear infections, and paw licking suggests allergic disease.

See your vet urgently if:

Rapid, widespread hair loss over days to weeks (may indicate a drug reaction, immune-mediated condition, or severe systemic illness)
Hair loss accompanied by open, draining wounds or deep skin infections
Hair loss combined with significant weight gain, lethargy, and intolerance to cold (evaluate for hypothyroidism urgently)
Hair loss with increased thirst, urination, panting, and a pot-bellied appearance (evaluate for Cushing's disease)
Circular, scaly patches of hair loss in a household with children or immunocompromised individuals (rule out ringworm, which is zoonotic)
Hair loss in a puppy that is also failing to thrive or has generalized skin disease

Treatment and Management

Treatment depends entirely on the underlying cause, which is why accurate diagnosis is essential before starting treatment:

Treating Allergic Hair Loss

When allergies are driving the hair loss through chronic scratching and licking, the priority is controlling the itch and treating any secondary skin infection. Allergy management with Apoquel, Cytopoint, or immunotherapy addresses the root cause. Our Itchy Skin Relief Spray can help break the scratch cycle while you pursue allergy diagnosis.

Hormonal Treatment

For hypothyroidism, daily levothyroxine supplementation is the standard treatment and typically produces visible coat improvement within 2 to 3 months. For Cushing's disease, treatment depends on the type and may include trilostane, mitotane, or surgery.

Treating Infections

Bacterial infections require appropriate antibiotics, ideally guided by culture results. Ringworm requires systemic antifungal medication for a minimum of 6 to 8 weeks, plus topical treatment and environmental decontamination. Demodex mange responds well to isoxazoline parasiticides.

Managing Genetic Conditions

Color dilution alopecia and seasonal flank alopecia have no cure but are cosmetic conditions. Keeping the skin moisturized, preventing secondary infections, and using melatonin supplementation (for seasonal flank alopecia) are the main management strategies.

Nutritional Support

Supporting coat regrowth with omega-3 fatty acid supplementation (EPA and DHA from fish oil) can improve hair quality and reduce inflammatory skin disease. Ensure the dog is on a complete, balanced diet with adequate protein.

Hair falling out and skin irritated? Start here.

If your dog is scratching or licking themselves bald, a topical antimicrobial spray can treat secondary infection, reduce itch, and protect the damaged skin while you investigate the root cause. Our Itchy Skin Relief Spray applies in seconds and is gentle enough for daily use on irritated skin.

Shop Itchy Skin Relief Spray

Related Conditions

This symptom can be a sign of several underlying conditions. Our in-depth guides cover each one:

Atopic Dermatitis in Dogs, the most common cause of itch-driven hair loss
Demodex Mange in Dogs, mite-driven hair loss from follicular damage
Fungal Skin Infections in Dogs, ringworm and other fungal causes of alopecia
Dog Allergy Testing Guide, identifying the allergy behind chronic scratching and hair loss
Dog Food Ingredients That Cause Skin Problems, food allergies as a driver of coat damage

Dog Hair Loss FAQ

Q: Is it normal for dogs to shed a lot?

Shedding is completely normal and varies enormously by breed, season, and individual. Double-coated breeds shed heavily, especially during spring and fall coat changes. Shedding is different from hair loss: shedding is a uniform thinning that maintains a normal coat pattern, while pathological hair loss creates bald patches, uneven coat, or visible skin.

Q: Can stress cause hair loss in dogs?

Stress can contribute to hair loss in two ways. Psychogenic alopecia (stress-related licking and chewing) is a behavioral condition. Telogen effluvium is a condition where a stressful event pushes a large number of hair follicles into the resting phase simultaneously, causing diffuse shedding 1 to 3 months after the event. Both are diagnoses of exclusion.

Q: Will my dog's hair grow back?

In most cases, yes. Hair loss caused by allergies, infections, and hormonal imbalances typically regrows once the underlying cause is treated. Exceptions include color dilution alopecia, scarring from deep infections, and some immune-mediated conditions that permanently destroy hair follicles.

Q: Should I change my dog's food if they are losing hair?

A diet change alone is unlikely to resolve hair loss unless food allergy is the underlying cause. If food allergy is suspected, a proper elimination diet trial (8 to 12 weeks) is needed. However, ensuring adequate omega-3 fatty acids and high-quality protein can support coat health regardless of the cause.

Q: When should I see a dermatologist instead of a general vet?

Consider a veterinary dermatologist if: the hair loss has not responded to initial treatment, the cause remains undiagnosed after basic testing, the hair loss is widespread or rapidly progressing, or your dog has a complex pattern involving multiple body systems.

Q: Can supplements help with hair loss?

Omega-3 fatty acids (fish oil) have the strongest evidence for supporting skin and coat health. Biotin has limited evidence in dogs. Zinc deficiency can cause hair loss, but supplementation only helps if there is a true deficiency. Supplements support treatment but do not replace diagnosis.

Sources

Miller WH Jr, Griffin CE, Campbell KL. Muller and Kirk's Small Animal Dermatology. 7th ed. Elsevier; 2013.

Scott DW, Paradis M. "A survey of canine and feline skin disorders seen in a university practice." The Canadian Veterinary Journal. 2001;42(8):638-644.

Frank LA. "Comparative dermatology: canine endocrine dermatoses." Clinics in Dermatology. 2006;24(4):317-325.

Mueller RS, et al. "Treatment of demodicosis in dogs: 2011 clinical practice guidelines." Veterinary Dermatology. 2012;23(2):86-e21.

Moriello KA, et al. "Diagnosis and treatment of dermatophytosis in dogs and cats." Veterinary Dermatology. 2017;28(3):266-e68.