Why is my dog losing hair?

When a dog starts losing hair, most owners want a clear, practical path: what likely caused it, whether it’s urgent, and what to try right away. The goal here is to help you recognize common patterns, understand what the skin and coat are doing, and follow a realistic sequence from at-home checks to veterinary evaluation if needed.

From light shedding to bald spots: common situations dog owners face

If you just brought a dog home — from a shelter, breeder, or rescue — and notice unfamiliar shedding or bald spots, you need guidance that balances calm observation with quick action. I typically see recently adopted dogs who shed because of stress, change in diet, or undiagnosed parasites; those situations often improve with short-term care but sometimes need testing.

Owners who report sudden, patchy, or progressively thinning coats are often worried about underlying disease. You will want to know whether the pattern suggests simple moulting or something requiring medicines. A few specific details — how fast the hair fell out, whether the skin is itchy or red, and whether other dogs in the home are affected — usually points the way.

Groomers, breeders, and volunteers who assess many coats need a quick checklist: is the cause primarily environmental and reversible, or is expert diagnosis needed? You may be deciding whether to change grooming frequency, try different products, or refer the dog to a veterinarian. Practical next steps and an evidence-based triage help avoid unnecessary treatments and protect the animal and others in communal settings.

If your dog is losing hair right now — likely causes to consider

In most cases the likeliest reasons are straightforward. Seasonal shedding and normal coat-cycle changes often account for a lot of loose hair, especially in double-coated breeds. External parasites such as fleas and various mites, or fungal infections like ringworm, commonly produce patchy hair loss that may be itchy. Allergies — to food, pollen, or topical products — tend to cause redness and scratching that results in hair thinning. Less commonly, hormonal imbalances such as hypothyroidism or Cushing’s disease, and stress-related overgrooming, can cause more persistent or generalized hair loss.

How you decide what’s most likely depends on pattern, timing, and symptoms. Even with similar-looking hair loss, the treatments differ: a flea problem needs insect control; ringworm needs antifungal therapy and environmental cleaning; allergies may respond to diet change or allergy testing; endocrine disease usually needs blood tests and specific medications.

Coat biology 101: how hair grows, cycles and sheds

Dog hair goes through repeating growth phases that influence how and when hair falls out. Individual hairs cycle through growth (anagen), brief transition (catagen), and rest/shedding (telogen) phases. A spike in telogen hairs — from seasonal cues, stress, or illness — will increase visible shedding without permanently damaging follicles, which is why many dogs regrow hair once the trigger resolves.

The skin does more than hold hair; it acts as a barrier and helps regulate temperature. Sebaceous glands coat hairs with oils that protect follicles; if oil production or skin thickness changes, the coat can look dull or patchy. Hormones influence both hair cycling and sebaceous activity, so low thyroid output or abnormal adrenal hormones may slow hair growth and change coat texture.

The immune system can also target hair follicles, either because of allergy or autoimmune processes. Inflammation around follicles impairs the normal cycle and may lead to breakage or permanent loss if severe. Overgrooming — whether from itch, anxiety, or boredom — physically removes hair and inflames skin, further disrupting follicles and sometimes creating a cycle of more licking and more hair loss.

Is the environment to blame? Heat, allergens and grooming effects

Day length and temperature shifts are reliable triggers for moulting in many breeds. Spring and fall are common times to see heavier shedding as dogs replace undercoats for seasonal insulation. Indoor heating or continuous air conditioning can blunt those natural rhythms and sometimes make the shedding pattern less obvious, but the underlying biology still responds to light and temperature changes.

Humidity and climate matter. Dry skin in low-humidity environments may flake and shed more, while humid warm conditions can favor parasites and yeast overgrowth that lead to patchy coating problems. A recent change — a new diet, a different shampoo, or moving to a new home — often precedes skin reactions, and those exposures are worth reviewing before jumping to advanced diagnostics.

Exposure risks include contact with other animals, contaminated bedding, or wildlife. Fleas can come from a neighbor’s yard; ringworm spores persist on brushes and blankets; communal housing such as shelters or doggy daycares raises the chance of contagious skin problems. Identifying recent exposures helps prioritize testing and isolation when necessary.

When to worry: warning signs that require veterinary care

Not all hair loss is an emergency, but some patterns require prompt veterinary attention. Rapid or patchy alopecia accompanied by sores, scabs, or bleeding suggests active infection, parasite burden, or severe self-trauma and should be evaluated quickly. Intense itching with open wounds increases the risk of bacterial infection and pain.

Systemic signs — fever, weight loss, lethargy, or changes in drinking and urination — may indicate an internal problem such as endocrine disease or a systemic infection and are reason to seek veterinary care without delay. Hairless patches in multiple body regions, especially if hair is thin rather than just dirty or matted, can suggest a metabolic or immune disorder.

Poor wound healing, recurrent skin infections, or hair loss that continues despite basic home measures are additional red flags. If you see any of these, prepare to share a thorough timeline and provide samples or photos to your veterinarian to speed diagnosis.

A practical owner checklist: what to do next, step by step

1. Document the problem. Take dated photos from multiple angles, note when you first saw hair loss, whether it’s getting worse, and whether other pets are affected. Small details — recent medications, new cleaners, or contact with other animals — often narrow the likely causes.

2. Perform simple checks. Use a fine-toothed flea comb over a white surface to look for adult fleas or flea dirt. Gently examine the skin for redness, scaling, or broken hairs. Note how much your dog is scratching, licking, or chewing and where the behaviour is focused.

3. Try short-term, low-risk measures. A single gentle bath with a hypoallergenic, non-medicated shampoo can remove allergens and surface organisms; avoid medicated products unless advised. Review diet history and recent treats; if a food allergy is plausible, avoid sudden ingredient changes but don’t start long elimination trials without planning.

4. Plan a veterinary visit if the problem is rapid, worsening, or has red flags. Bring photos, a list of recent exposures and products used, and any sample material you collected (loose hair, scabs). Ask the clinician about basic diagnostics they can perform in clinic: skin scrape for mites, tape prep or cytology for bacteria and yeast, fungal culture for ringworm, and bloodwork to screen for endocrine disease.

5. Follow the recommended course and monitor. If your veterinarian prescribes topical or systemic therapy, follow instructions closely and keep photographing progress every one to two weeks so you can tell whether the coat is improving.

Home fixes that work: managing environment and behavior

Preventing further irritation and supporting regrowth means tackling both the physical environment and the dog’s behaviour. Consistent, veterinarian-approved flea and tick prevention is one of the most effective single actions; treating all in-contact animals and washing bedding in hot water reduces reinfestation.

Adjust grooming to the dog’s needs: for double-coated breeds, avoid over-shaving the undercoat and use appropriate de-shedding tools rather than harsh clipping. Use soft brushes on irritated skin and choose gentle, pH-balanced shampoos when bathing. If mats are present, have them professionally removed to avoid cutting or tearing the skin.

Stress reduction matters. Predictable daily routines, regular exercise, and enrichment that engages the nose and body can reduce anxious licking or chewing. If the behaviour appears compulsive or driven by anxiety, discuss behavioural strategies or a behaviourist referral with your veterinarian.

If a food allergy is suspected, plan a gradual, veterinary-guided elimination trial using a limited-ingredient or hydrolyzed diet for several weeks. Sudden diet changes can complicate interpretation; do not start over-the-counter “novel” diets without consultation if the dog has multiple exposures or suspected severe allergy.

Grooming tools and safe products vets recommend

• Fine-toothed flea comb and a bright handheld magnifying light — helpful for detecting fleas, flea dirt, and tiny mites, and for close inspection of scabs and broken hairs.

• Non-medicated hypoallergenic shampoo and a soft bristle brush — use these for gentle cleansing and to remove surface allergens without irritating the skin.

• Disposable gloves, sealable sample containers or plastic bags, and a phone or camera for clear, dated photos — these make it easier to show your veterinarian the history and to transport samples like loose hair or crusts when requested.

• A record sheet (paper or app) to note onset, progression, behaviours, and products used — this often speeds diagnosis and avoids repeated questioning at appointments.

• Avoid using unprescribed steroids, topical pesticides, or human skin products without veterinary advice; these can mask signs, worsen infections, or be toxic to dogs.

References and expert sources

• Merck Veterinary Manual: “Alopecia (Hair Loss) in Dogs” — clinical overview and diagnostic approach
• American College of Veterinary Dermatology (ACVD): client information sheets and dermatologist referral directory
• Cornell University College of Veterinary Medicine, Dermatology Service: “Canine Dermatology – Common Skin Conditions”
• UC Davis Veterinary Medicine, Dermatology Service: clinical guides on parasitic and fungal skin disease in dogs
• Iowa State University, College of Veterinary Medicine: “Canine Skin Diseases — Diagnostic Tests and Treatment Guidelines”