Understanding Hair Loss in Dogs
All dogs shed to some degree, but when hair loss becomes patchy, symmetrical, excessive, or is accompanied by scratching, skin changes, or other symptoms, something more than normal moulting is likely at play. Alopecia — the medical term for hair loss — in dogs has a wide range of causes, from the benign and temporary to the complex and chronic. Identifying the underlying cause is the key to effective treatment.
This guide covers the most common causes of canine alopecia, ranked broadly by frequency, along with information on how vets diagnose the cause and what treatment options are available.
Most Common Causes of Hair Loss in Dogs
1. Seasonal Shedding and Coat Blowing
The most common reason for increased hair loss in dogs is entirely normal: seasonal shedding. Double-coated breeds such as German Shepherds, Huskies, Golden Retrievers, and Border Collies shed their undercoat dramatically in spring and to a lesser extent in autumn — a process sometimes called "coat blowing." This produces enormous amounts of loose hair but should not result in visible bald patches. If the skin beneath looks healthy and the coat regrows evenly, no intervention is needed beyond regular brushing and a good diet.
2. Allergies (Environmental, Food, and Flea Allergy Dermatitis)
Allergic skin disease is one of the leading causes of pathological hair loss in dogs. Affected dogs scratch, lick, chew, and rub at itchy areas until the coat breaks and thins. Three main types are responsible:
- Flea allergy dermatitis (FAD): An allergic reaction to flea saliva, causing intense itching and hair loss typically over the lower back, rump, and tail base. Even a single flea bite can trigger a severe reaction in sensitised dogs. ESCCAP recommends year-round flea prevention in most European climates, as flea populations now persist indoors through winter.
- Environmental (atopic) allergy: A reaction to inhaled or contact allergens such as pollen, dust mites, or mould spores. Typically causes itching of the paws, face, ears, and armpits, with secondary hair loss from self-trauma.
- Food allergy: Adverse reactions to dietary proteins (commonly chicken, beef, dairy, or wheat) cause non-seasonal itching and hair loss, often with concurrent gastrointestinal signs.
Diagnosis involves elimination diets (for food allergy), intradermal or blood allergy testing (for atopy), and thorough parasite control. Treatment ranges from antiparasitic products and dietary management to immunotherapy (desensitisation injections) and targeted medications such as oclacitinib (Apoquel) or lokivetmab (Cytopoint).
3. Parasites: Mange (Demodex and Sarcoptes)
Two types of mange mite cause significant hair loss in dogs:
- Demodectic mange (Demodex canis): Caused by Demodex mites that normally live in small numbers in hair follicles. In puppies or immunocompromised adults, mite numbers proliferate and cause patchy to generalised hair loss, typically beginning around the face, muzzle, and forelegs. It is not contagious to other dogs or humans. Localised cases in puppies often resolve spontaneously; generalised cases require antiparasitic treatment.
- Sarcoptic mange (Scabies): Caused by the highly contagious Sarcoptes scabiei mite. It causes intense itching, crusting, and hair loss, particularly on ear margins, elbows, hocks, and the ventral abdomen. It is contagious between dogs and can cause temporary skin reactions in humans. Diagnosis is via skin scrapes or treatment response; treatment involves licensed acaricide products. ESCCAP guidelines provide detailed parasite control recommendations across European countries.
4. Ringworm (Dermatophytosis)
Despite its name, ringworm is a fungal infection (typically Microsporum canis or Trichophyton species), not a worm. It causes circular patches of hair loss with scaling, broken hairs, and sometimes mild inflammation. It is highly contagious between animals and to humans (a zoonosis), making prompt treatment essential in multi-pet households. Diagnosis is via fungal culture, Wood's lamp examination, or PCR testing. Treatment involves antifungal shampoos, topical creams, and systemic antifungal medication in widespread cases. Environmental decontamination is critical to prevent reinfection.
5. Hypothyroidism
An underactive thyroid gland is one of the most common hormonal causes of hair loss in dogs, particularly in medium to large breeds in middle age — Dobermanns, Golden Retrievers, Cocker Spaniels, and Irish Setters are among the breeds with higher prevalence. Thyroid hormone is essential for normal hair follicle cycling; deficiency causes a bilaterally symmetrical, non-itchy hair thinning and loss, often beginning on the trunk and sparing the head and limbs. The coat becomes dry, brittle, and dull, and the skin may darken (hyperpigmentation) and thicken.
Other signs include weight gain despite unchanged appetite, lethargy, cold intolerance, and a "tragic expression" caused by facial muscle and skin changes. Diagnosis is confirmed with a blood test measuring thyroid hormone (total T4 and ideally free T4). Treatment with daily oral levothyroxine is highly effective — coat quality and energy levels typically improve significantly within two to three months.
6. Hyperadrenocorticism (Cushing's Disease)
Cushing's disease — excess cortisol production, most commonly from a pituitary gland tumour — causes a characteristic pattern of hair loss and skin changes. Affected dogs develop a pot-bellied appearance, drink and urinate excessively, pant heavily, and develop thin, fragile skin with poor wound healing. Hair loss is typically bilateral and symmetrical on the trunk, with sparing of the head and legs. The skin may show calcinosis cutis (calcium deposits) and comedones (blackheads).
It primarily affects middle-aged to older dogs, and Poodles, Dachshunds, Yorkshire Terriers, and Boxers are among the breeds at higher risk. Diagnosis involves blood cortisol testing (LDDS or HDDS test) and imaging. Treatment depends on the underlying cause: oral trilostane or mitotane for pituitary-dependent disease, and surgery or radiation for adrenal tumours.
7. Stress and Psychogenic Alopecia
Although less common in dogs than in cats, chronic stress and anxiety can cause hair loss through compulsive licking and chewing of specific body areas — typically the forelegs (acral lick dermatitis) or flanks. The resulting lesions are wet, thickened, and heavily licked. Addressing the underlying anxiety through behavioural modification and environmental enrichment, alongside treating any secondary skin infection, is the foundation of management.
Diagnosis: What Your Vet Will Do
Diagnosing the cause of alopecia requires a thorough approach. Your vet will take a detailed history — onset, distribution, seasonality, diet, parasite prevention, and any other symptoms — and perform a full skin examination. Tests may include:
- Skin scrapes (to identify mange mites)
- Fungal culture or Wood's lamp (for ringworm)
- Cytology of skin surface (for infection)
- Blood tests including thyroid panel, cortisol testing, and full biochemistry
- Elimination diet trial (for food allergy)
- Skin biopsy (in complex or atypical cases)
- Allergy testing (intradermal or serology)
See Your Vet If...
- You notice patchy, circular, or symmetrical bald areas on your dog's coat
- Hair loss is accompanied by scratching, licking, or chewing
- The skin beneath lost hair looks red, scaly, crusty, thickened, or darkened
- Other pets or people in the household are also developing skin lesions (suggests ringworm or sarcoptic mange)
- Hair loss is accompanied by weight changes, lethargy, excessive thirst, or panting
- Hair loss continues to spread or worsen
Hair loss in dogs is rarely cosmetic — it almost always reflects an underlying health issue. Early diagnosis and treatment give the best chance of full coat recovery and significantly improve your dog's comfort and quality of life.