Why is my dog losing hair in patches?
Patchy hair loss in dogs is most often driven by flea allergy dermatitis, environmental allergies (atopy), demodectic or sarcoptic mange, or a hormonal condition like hypothyroidism or Cushing's disease. If the hair loss is symmetric on both sides of the body, is spreading fast, or comes with thickened dark skin and a musty smell, book a vet within the week for skin scrapes and bloodwork.
This page is general pet health information, not a diagnosis or treatment plan for your pet. Always confirm anything urgent with a licensed veterinarian.
When to see a vet today
See a vet today if you notice Rapidly spreading bald patches with crusts and pus, Symmetric hair loss on both flanks with a pot-belly and increased thirst (possible Cushing's), and Intense itch that stops your dog from sleeping. These are the signs that should not wait for home care or a watch-and-see approach. If any of them appear, skip the rest of this guide and call your vet or an emergency clinic now - waiting is the risky option.
- ●Rapidly spreading bald patches with crusts and pus
- ●Symmetric hair loss on both flanks with a pot-belly and increased thirst (possible Cushing's)
- ●Intense itch that stops your dog from sleeping
- ●Ring-shaped crusty patches in a puppy or an immunocompromised human household member (ringworm)
Safe to monitor at home
Milder signs are usually safe to watch for a day or two: Seasonal mild thinning during a coat blow in spring/autumn and Slight thinning at pressure points (elbows, hocks) on hard flooring. Keep notes and photos so you can spot a trend. Anything that worsens, spreads, or comes with appetite, energy or behavior changes moves out of this category and into a vet visit.
- ●Seasonal mild thinning during a coat blow in spring/autumn
- ●Slight thinning at pressure points (elbows, hocks) on hard flooring
What to photograph or record
Photograph or record Wide shot of the whole dog from both sides for pattern, Close-up of one representative bald patch with a coin next to it for scale, and Part the hair at the edge of the patch and photograph the skin surface in good, even light. Clear, well-framed evidence is what lets a vet - or a PetSenseAI scan - judge the change instead of guessing from a description. The checklist below is the exact shot list.
- Wide shot of the whole dog from both sides for pattern
- Close-up of one representative bald patch with a coin next to it for scale
- Part the hair at the edge of the patch and photograph the skin surface
- Photograph the belly, groin, and under the tail - flea allergy always shows there
Likely causes
The causes vets consider first for this presentation are flea allergy dermatitis, atopy (environmental allergy), demodectic mange, and sarcoptic mange (scabies). Most are manageable once identified, but they look similar from the outside, which is why a photo-based triage and, when needed, an exam matter more than guesswork.
Flea allergy dermatitis
Number-one cause. Hair loss at the base of the tail, thighs, and belly. Even one bite triggers it in sensitised dogs.
Atopy (environmental allergy)
Face, paws, ears, armpits, groin. Chronic licking of paws is a giveaway.
Demodectic mange
Puppy or immunocompromised adult. Bald patches around the eyes and lips. Not contagious.
Sarcoptic mange (scabies)
Intensely itchy, ear tips, elbows, belly. Highly contagious to other dogs and briefly to humans.
Ringworm
Fungal, not a worm. Ring-shaped crusts. Contagious to people and cats.
Hormonal (hypothyroid, Cushing's)
Middle-aged and older dogs. Symmetric truncal loss, no itch, dull coat, skin changes color.
Safe home care
For mild cases, safe home care is verify flea control is current for every pet in the home and treat the environment, bathe with a gentle oatmeal or chlorhexidine shampoo if your vet has ruled out mange, and photograph patches weekly with a coin for scale - an objective baseline helps the vet track response to treatment. These steps comfort and monitor; they do not treat the underlying cause. Stop home care and call a vet if anything in the urgent list above appears or the trend moves the wrong way.
- -Verify flea control is current for every pet in the home and treat the environment
- -Bathe with a gentle oatmeal or chlorhexidine shampoo if your vet has ruled out mange
- -Photograph patches weekly with a coin for scale - an objective baseline helps the vet track response to treatment
- -Wash bedding weekly at 60°C to reduce mite and fungal load
PetSenseAI is a triage and monitoring tool, not a substitute for veterinary care. Always confirm treatment plans with a licensed veterinarian.
Frequently asked
Can dog hair loss be caused by stress?
Rarely as the sole cause, but stress makes underlying allergies and dermatitis flare. Over-grooming from anxiety usually shows as thinning on the flanks or feet without inflamed skin - a diagnosis of exclusion after allergies, mites, and hormones are ruled out.
Will my dog's hair grow back after mange or ringworm?
Yes in most cases, once the underlying cause is treated. Expect regrowth over 4–8 weeks. Scar tissue from severe secondary infections may leave permanent thin patches.
Is my dog's hair loss contagious to me?
Sarcoptic mange and ringworm can transfer to humans. Demodectic mange, allergies, and hormonal alopecia cannot. Wash hands after handling and cover any skin lesions of your own until the diagnosis is clear.
What tests will the vet run for hair loss?
Typically skin scrapes for mites, a fungal culture or Wood's lamp for ringworm, tape impressions for yeast and bacteria, and - if the loss is symmetric - thyroid and adrenal bloodwork. A biopsy is reserved for cases that don't respond to standard treatment.
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Start a scanPetSenseAI is an AI-assisted triage and monitoring tool. It does not diagnose, treat, cure, or prevent any condition. Always consult a licensed veterinarian for any medical concern about your pet.
If your pet is in distress - collapse, laboured breathing, seizures, uncontrolled bleeding, suspected poisoning, bloat, or trauma - stop and contact an emergency veterinarian or a poison control line immediately. Do not wait for a scan result.