Seeing your dog lose hair in patches, especially when scabs are present, is always concerning.
Patchy hair loss combined with crusts or sores almost always means something is irritating the skin, causing inflammation, infection, or excessive scratching.
We outline the common causes of patchy hair loss and scabs in dogs, what you can do, and when to seek veterinary help.
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Dog Losing Hair in Patches and Scabs — Why It Happens
Dogs lose hair in patches and develop scabs when something inflames or irritates the skin and leads to scratching, biting, or infection. This can be caused by allergies, mites, fungal infections, flea bites, hormone disorders, or bacterial infections that form when the skin becomes damaged.
Once the irritation begins, dogs scratch or chew the area, worsening the bald patches and causing scabs to form. Many conditions start mildly but progress quickly if untreated.
Understanding what triggers the irritation is key to stopping the cycle and helping the skin heal.
Dog Losing Hair in Patches and Scabs: Common Causes
Flea Allergy Dermatitis (FAD)
Flea allergy dermatitis is the most common cause of patchy hair loss and scabs in dogs. Even a single flea bite can trigger an intense allergic reaction in sensitive dogs. When a flea bites, it injects saliva into the skin — and this saliva causes extreme itching for allergic dogs.
They bite, scratch, and chew at the affected area, often focusing around the base of the tail, hind legs, stomach, and lower back.
Over time, repeated scratching leads to bald patches, scabs, crusty bumps, and redness. The skin may feel warm or thickened from chronic irritation.
Even if you don’t see fleas, they may still be the cause — fleas move quickly and spend most of their time hiding in bedding, carpets, and outdoor areas.
Flea allergies worsen rapidly and often need a combination of flea control, anti-itch relief, and skin healing treatments.
Environmental or Food Allergies
Allergies to pollen, dust mites, mold, grass, or food ingredients are major causes of hair loss in patches accompanied by scabs.
Allergies make the skin extremely itchy, and dogs often lick or chew certain “hot spots” until the hair falls out and sores form.
Environmental allergies usually flare seasonally and affect the paws, underarms, belly, and ears.
Food allergies, on the other hand, often cause year-round itching, especially around the face, paws, and belly. Dogs may develop oozing hot spots that scab over, leading to uneven hair loss.
Because allergies cause chronic inflammation, the skin becomes more vulnerable to secondary infections, which worsen the scabbing and bald areas.
Mange (Demodectic or Sarcoptic Mites)
Mange is one of the most dramatic causes of patchy hair loss and scabs. Microscopic mites burrow into the skin, causing severe irritation.
Demodectic mange often causes circular bald spots with red, scaly skin. Sarcoptic mange (scabies) is intensely itchy and highly contagious, typically causing widespread hair loss, thick scabs, and constant scratching.
Dogs with mange often have crusty patches on the elbows, face, ears, belly, or around the tail.
As the dog scratches, the skin becomes raw and infected, creating more scabs and spreading the bald patches. Mange progresses rapidly without treatment and can severely damage the skin barrier.
Ringworm (Fungal Infection)
Despite the name, ringworm is not a worm — it’s a highly contagious fungus that causes circular areas of hair loss with scaly edges.
These bald patches often look like rings with red centers and crusty borders. Many dogs develop scabs as they scratch the irritated skin or when the skin becomes infected.
Ringworm spreads easily to other pets and even humans. Because the fungus lives on the hair shaft and skin surface, it causes hair to fall out in clumps, leaving patchy bald areas that look dry, brittle, and flaky. Dogs in shelters, puppies, and dogs with lowered immunity are most at risk.
Bacterial or Yeast Skin Infections
When the skin becomes irritated from allergies, moisture, parasites, or grooming habits, bacteria or yeast multiply rapidly.
These infections often create moist, inflamed patches of skin that quickly turn into crusts or scabs. Hair around the infected area falls out easily, leaving irregular bald spots.
Yeast infections smell musty, while bacterial infections often produce pus-filled bumps that scab over.
Dogs may lick or scratch constantly, worsening the damage and causing the infection to spread. Without treatment, these infections deepen into the skin and create layers of scabbing.
Hormonal Disorders
Hormone disorders can cause symmetrical patchy hair loss that may turn scabby if the skin becomes irritated. Hypothyroidism slows hair growth and leads to thin, brittle fur that falls out easily, especially on the sides, neck, and tail.
Cushing’s disease, caused by excess cortisol, thins the skin and makes it fragile. Even mild scratching can create sores or scabs. Because hormones affect the immune system, dogs with endocrine disorders are prone to bacterial or yeast infections that cause scabbing and patchy bald spots.
While hormonal causes usually create less itching than allergies or parasites, the hair loss is more persistent and widespread.
What to Do If Your Dog Is Losing Hair in Patches and Has Scabs
Start by examining your dog’s skin closely. Look for fleas, small bumps, redness, or areas where the skin feels warm or thick. If fleas are present or suspected, begin a fast-acting flea treatment and wash bedding thoroughly.
For dogs with hot spots or irritated patches, you can gently clean the area with a mild antiseptic solution and trim fur around the sore to let it breathe.
A bland diet may help if food allergies are suspected, but changes should be made gradually. If your dog is licking or scratching aggressively, an Elizabethan collar can protect the skin as it heals.
Keeping your dog’s coat clean and dry helps prevent infections from worsening. Avoid using human creams or ointments unless instructed by your veterinarian — some products can trap bacteria or irritate the skin further.
Probiotics and omega-3 fatty acids may help support skin health, but they work best alongside proper diagnosis and treatment.
When to Call or Visit Your Vet
You should contact your veterinarian anytime hair loss and scabs appear suddenly, worsen quickly, or do not improve within a few days. Conditions like mange, ringworm, and severe allergies require prescription medications to resolve.
Seek veterinary care urgently if your dog has:
• Bleeding or oozing sores
• Thick yellow scabs
• Rapidly expanding bald patches
• Intense itching that interferes with sleep
• Signs of pain when touched
• A foul smell from the skin
• Loss of appetite or lethargy alongside hair loss
Because many causes are contagious or chronic, early diagnosis prevents long-lasting skin damage and stops the spread to other pets or household members.
Read more: Dog shedding excessively (What’s causing it?)
Read more: Dog Losing Hair on Legs (Common reasons explained)
Related: Dog losing hair in patches on back (Here’s why)
Key Takeaway
When a dog loses hair in patches and develops scabs, it’s almost always a sign of skin irritation, infection, parasites, or allergies.
While mild cases can improve with good home care, many underlying causes require veterinary treatment to fully resolve.
The sooner the skin is assessed and treated, the faster your dog’s hair will regrow — and the more comfortable they’ll feel.