Cat with Sores and Bald Patches/Hair Loss in Cats, Dog with Sores and Bald Patches/Hair Loss in Dogs

Sores and hair loss in pets may be caused directly by a disease or infection, or by pets scratching and biting their skin because they’re itchy due to fleas or other infestation (lice, mites, etc.), allergies, or infection.

The most common causes of sores, scabs, bald patches, and hair loss in cats and dogs are parasites, infections, allergies, emotional problems,  dietary problems, and pyotraumatic dermatitis, though there are a number of other possibilities as well, including sunburn, skin cancer, feline facial alopecia, telogen effluvium, stud tail, hormonal disease, acne, puppy strangles, and other conditions.

Fleas and Other Parasites

Risk Factors: Going outdoors, contact with other animals, warm environment, humidity

Fleas are among the most common causes of sores and bald patches on pets, particularly on their backs, inner thighs, groin area, and neck area. You can test for fleas by combing your cat or dog thoroughly and placing any debris from the comb onto a piece of damp white paper towel or tissue. If there are brown specks that are soon surrounded by reddish rings when they absorb water from the paper, they are probably flea excrement. Other parasites such as mites (a cause of mange/scabies, and other problems) and lice, as well as bites from mosquitos and ticks, may also cause sores. Outdoor pets are particularly likely to suffer bites and infestations.

Treatment varies based on the type of parasite, but typically involves eliminating the parasite from the pet and making sure that the home is also clear of adult parasites and eggs. In the case of fleas, by far the most common external parasite, combing the cat or dog thoroughly with a flea comb and dropping the fleas into a bowl of hot, soapy water is the first line of defense. There are also various topical and oral medications that can be used to remedy aggressive problems. To keep fleas away, the house must also be cleared of both adults and eggs.


Risk Factors: Going outdoors, pet not spayed or neutered (which increases the risk of fights), contact with other animals, contact with people who have infections that can be passed to cats and dogs (such as ringworm)

There are a variety of infections that can cause hair loss and sores in pets. Ringworm, a common fungal infection, causes red rings, scaly or crusty skin, hair loss, and/or sores. This disease is highly contagious to other pets and people (See Ringworm Symptoms and Treatment for more on this infection).

External injuries may also become infected, or a foreign body (such as a thorn) may become embedded in the skin, causing infection. Abscesses, which create open, weeping sores when they burst, are caused by bacterial infections. Pets often suffer abscesses after being bitten by other animals. Cats may also suffer skin lesions when infected with the feline leukemia virus (FeLV).

There are many other types of infection that may cause sores, scaly or flaking skin, and hair loss, and treatment will depend on the type of infection. For example, bacterial infections are treated with antibiotics, whereas fungal infections require antifungals. Additional treatments may also be required, such as moving a foreign body from beneath the skin.

Allergies and Sensitivities

Risk Factors: Genetic predisposition, exposure to allergens

Dermatitis, a skin reaction often triggered by allergies, is characterized by red skin, bumps or sores, flaking skin, and/or hair loss. Although most commonly caused by flea bites, the reaction can also be triggered by contact with certain metals, rubber, plastic, wool, dyes, carpet deodorizers, chemicals, shampoos, poison ivy, and many other things. Pets may even react to certain medications or medical procedures. Additional allergies or sensitivities that may cause sores and hair loss include inhalant allergies (i.e., cigarette smoke, pollen, dust mites, mold, etc.) and food allergies.

Treatment may include eliminating the allergen or parasites and/or using special shampoos, topical ointments, antihistamine medications, corticosteroids, or dietary supplements, depending on the type and severity of the problem. Don’t give your pet any medication without first consulting a veterinarian to ensure safe and effective dosing.

Pyotraumatic Dermatitis

Risk Factors: Long fur, moving from a cold to hot climate, high humidity, breed disposition, stress, allergies

More commonly known as “hot spots,” this condition most often afflicts dogs with long, thick coats such as Golden Retrievers, Samoyeds, Cocker Spaniels, and Akitas. The problem is uncommon in cats, and when it does occur, it’s often a reaction to emotional stress.

Hot spots are itchy areas that become inflamed (red), oozy, and raw, and pets will bite or scratch them trying to get relief. Some experts believe that hot spots are caused by bites from fleas or other parasites, though it’s not known for sure. Other types of allergies may also trigger the problem. Hot spots can usually be treated with either a topical or injected medication.

Dietary Problems

Risk Factors: Low-fat diet; consuming foods that are more likely to trigger reactions (i.e., wheat, dairy); artificial dyes, additives, and preservatives in pet foods; eating cheap, bargain-brand pet foods

In addition to food allergies (which can often be treated by implementing a hypoallergenic diet), cats on low-fat diets can develop dry, flaky skin. This occurs because cats are obligate carnivores, which means that they require a higher proportion of fat in their diet than omnivores such as humans and dogs. Dry skin can in many cases be remedied with dietary changes and/or Omega-3 fatty acid supplements. There are Omega-3 supplements formulated for dogs as well, and many owners have found them beneficial. However, dry, flaky skin in dogs is more likely to be caused by allergies (including food allergies), parasites, or infections than dietary deficiencies. Don’t give supplements without first consulting a veterinarian who is aware of your pet’s medical history and state of health.

Personally, I don’t recommend low-fat diets to help cats lose weight. Cats are biologically designed to require a high-protein diet, rich in fats. Most cats become fat because cheap cat foods are filled with carbohydrates that they can’t use properly the way an omnivore can. For weight loss, I recommend a premium, high-protein wet food diet and encouraging more exercise (see How to Help Fat Cats Lose Weight for tips on how to do this).

Emotional Problems

Risk Factors: Breed disposition, nervous or high-strung temperament, boredom, insufficient attention from owners/being left on their own too often, major changes (i.e., moving house, new pet, new baby, new roommate), loss (i.e., death of a loved one), lack of stimulation (toys, playtime, exercise, etc.), conflicts with other pets

Bored or stressed pets may lick themselves to the point that sores form or pull out their own fur (when this latter condition is triggered by psychological factors rather than flea allergies or other medical causes, it’s called psychogenic alopecia). Pets that are chewing out their own hair usually attack the fur along their backs or abdomens. The problem is more common in high-strung or nervous dog and cat breeds. Always have your pet checked by a veterinarian for medical problems and infestations before assuming that the problem is psychological.

Treatment may involve spending more quality time with a pet, providing an enriched environment for indoor cats and more walks for dogs, removing stressors from a pet’s environment, and/or attaching a protective covering to the targeted area of the body until the habit is broken. Some people with nervous pets have also seen benefits using calming pheromone products such as Feliway for cats and D.A.P. for dogs.

Because the problem in cats is often triggered by stressful conflicts in multicat households, taking steps to reduce such conflicts is beneficial (see How to Prevent Cat Conflicts for more information). Distraction is also beneficial. Dogs may be distracted from the habit with appealing chew toys, and engaging cats and dogs in play sessions when they start to chew can help to break the habit.

In extreme cases, medications designed to treat obsessive-compulsive disorder may be prescribed. However, pharmaceutical intervention should be considered a last resort because medications have side effects and some are addictive.

Sunburn and Skin Cancer

Risk Factors: White/light coat or hairlessness, outdoor access during peak sun times, summertime, hot climate

Cats and dogs with light-coloured coats (especially those with white ears) and hairless breeds that go outdoors may suffer nasty sunburns, particularly on their ears and noses. Signs of severe sunburn include redness and scaly skin over the afflicted areas that later may form crusts and/or ulcers.

Sunburns increase the risk of developing skin cancer. Skin cancer may present similarly to a parasitic or bacterial skin infection, causing hair loss, redness, flaky skin, itching, or sores (many common types of infection can look like cancer, so don’t panic if you see sores, but do consult a veterinarian to be on the safe side). Skin cancer treatments include surgical removal of afflicted areas, chemotherapy, radiation therapy, and photodynamic therapy.

Sunburns can be prevented and the risk of cancer reduced by keeping pets indoors during peak sun hours.

Feline Facial Alopecia

Risk Factors: Short fur, dark coat, age 14-20 months

There is a normal condition that causes cats to lose hair above their eyes (between the eyes and ears). This condition, which typically arises between 14 and 20 months of age, is more common in cats with short fur and dark coats. Assuming that the skin is healthy looking, it’s not a health problem and requires no treatment. However, if there are any sores, scaliness, redness, or other problems visible on the hair loss site, a veterinarian should be consulted.

Telogen Effluvium

Risk Factors: Pregnancy, nursing

Dogs and cats often shed a significant portion of their coats when pregnant or nursing, a phenomenon referred to as “blowing her coat.” In such cases, the hair may actually come out in clumps. The coat grows back, though sometimes the new coat has a slightly different texture, decreased density, or a darker colour.

Stud Tail

Risk Factors: Male, unneutered

Stud tail, an infection of the supracaudal gland, is a common problem in unneutered male animals (though it occasionally afflicts neutered males and females). This condition causes hair loss near the base of the tail and oily, crusty skin coated in a foul-smelling waxy substance. Sometimes the site becomes infected. Treatments may include the use of medications and special shampoos.

Hormonal Disease

Risk Factors: Middle age to old age, breed disposition/genetic vulnerability, dietary deficiency

Various hormonal diseases can cause hair loss and skin problems, including hyperthyroidism, hypothyroidism, and Cushing’s disease (hyperadrenocorticism). In such cases, hair loss is often symmetrical, running along the sides of the body. Additional symptoms differ depending on the condition. Hyperthyroidism (overactive thyroid) triggers hyperactivity and weight loss, whereas hypothyroidism (underactive thyroid) usually has the opposite effect. Cushing’s can trigger a mix of symptoms, for example, the increased appetite that is also seen with hyperthyroidism , the lethargy that usually characterizes hypothyroidism, and the potential to either gain or lose weight. A bulging stomach and increased thirst and urination often accompany Cushing’s disease as well.

Treatment depends on the type of disease. Hyperthyroidism is most effectively treated with radioactive iodine therapy, though there are also medications for this disease. Hypothyroidism is treated with medication, and Cushing’s is most effectively treated with surgery, though there are also medications available.


Risk Factors: Youth, breed disposition

Like people, cats and dogs can be afflicted with acne, which usually starts at five to eight months of age in dogs and around the one-year mark for cats. Acne typically manifests as red bumps and/or black heads, often on the lips and chin. These spots can become infected and itchy, causing pets to rub their faces against surfaces to relieve the itch. In dogs, the condition often improves over time; in cats, it may be lifelong but can go into remissions.

Acne can often be treated with special shampoos or benzoyl peroxide washes. Oral medications may also be required for serious cases. Keeping the chin clean and dry (cleaning it after the pet eats) may help in some cases. If you believe that your pet suffers from acne, consult a veterinarian to rule out more serious problems and develop an appropriate treatment plan.

Allergy to a rubber or plastic food bowl can cause similar symptoms to acne. In such cases, switching to a stainless steel bowl will solve the problem.

Eosinophilic Granulomas

Risk Factors: Allergies, breed disposition

Eosinophilic granulomas (also known as rodent ulcers) are painful or itchy yellowish-pink sores often found on the head, face, paw pads, thighs near the tail, and perineal region, though they may afflict other areas of the body as well. Resulting from immune system dysfunction, eosinophilic granulomas may be triggered by an allergic reaction, though causes are often unknown. Treatments include administering medication and, if food allergies are suspected, switching to a hypoallergenic diet.

Puppy Strangles

Risk Factors: Age = less than 4 months

Afflicting puppies under four months of age, juvenile pyoderma (also known as juvenile cellulitis, lymphadenitis, and most commonly, puppy strangles) causes skin inflammation or crusting dermatitis. Pustules, often around the muzzle, lip area, and inside the ears, drain and scab over. Muzzle swelling, joint pain, and fever accompany the illness.

Causes of juvenile pyoderma are unknown, and there are no preventive measures available, However, there are medications to treat puppy strangles effectively, and relapses after treatment are rare.

Other Conditions

There are many other rare conditions that can cause sores and/or hair loss in pets, for example, autoimmune disorders such as lupus and alopecia areata. However, such conditions are uncommon, whereas fleas, allergies, infections, and stress are the most common causes of sores and hair loss in cats and dogs.

For more cat articles, see the main Cats page. For more dog articles, see the main Dogs page.

This article is provided for informational purposes only and is not intended as a substitute for veterinary consultation and care.


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