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Intro to Pet Dermatology 101: Common Skin Conditions - Vet looking at a dog's skin through a magnifying lamp with owner by side

Common Skin Conditions in Dogs and Cats: Pet Dermatology 101

If you’ve ever been serenaded during the night by your dog’s relentless scratching or your cat vomiting hairballs as a result of overgrooming, you know that skin conditions can be some of the most frustrating for pet parents to deal with.

As a veterinarian, my goal is to help keep your furry family members happy and healthy. I have seen dogs and cats for a variety of reasons, but skin issues are among the most common. These issues include itchiness, ear infections, rashes, hair loss, fleas, lumps and bumps, and more.

Dr. Liza Cahn with dog

In Part 1 of this two-part Pet Dermatology series, we’ll dive into common skin issues in dogs and cats and what you (and your vet) can do about them.

The Skin They’re In

Skin is pretty amazing! Comprising 10-15% of your pet’s body weight, their skin is their largest organ. It is composed of three layers, including the hypodermis, which is mainly fatty tissue; the collagen-rich dermis, which contains sebaceous glands and hair follicles; and the epidermis, which contains cells that produce keratin, a protective waxy substance.

Your pet’s coat also consists of thousands of hair follicles, which, as we all know, undergo regular shedding. And that fur coat isn’t just for cuddles! Your pet's skin and coat protect their health by:

  • Offering a protective barrier against environmental hazards
  • Aiding in temperature regulation
  • Forming a vital part of the immune system that helps to prevent infection and disease
  • Maintaining their hydration
  • Serving as storage for nutrients such as proteins, fatty acids, vitamins, and minerals

Top 5 Skin Conditions in Dogs and Cats

1. Allergies

An allergy is an overreaction of the immune system to a substance that is usually harmless. While allergies in people often cause red eyes and sneezing, dogs and cats with allergies typically develop symptoms affecting their skin, such as itchy skin and recurrent skin and/or ear infections.

Common symptoms of allergies in dogs and cats include:

  • Skin irritation: Redness, rashes, inflammation, and infection, which can appear as pimples, scabs, or scales. (Seeing black spots on your pet’s chin or face? It might be pet acne)
  • Pruritus (AKA itchy skin): Relentless scratching, biting, and chewing at specific areas of the body or all over
  • Ear infections: Characterized by scratching, head shaking, debris, and odor in the ear canals
  • Hair loss: Due to constant scratching and licking, or the underlying condition itself
  • Sneezing and runny nose: Clear discharge from the eyes or nose may be a sign of environmental allergies in some cases
  • Gastrointestinal signs: Vomiting and diarrhea may occur with food allergies. Cats might also vomit hairballs as a result of overgrooming
Dog with allergy problems has swollen face and red puffy eyes (Dog with swollen face due to allergy)

Dogs and cats can be allergic to many different things. These allergens fall into three general categories.

Flea Allergies

While these little buggers will cause itching in any pet, some animals actually have an allergic reaction to the bite (saliva) of a flea — a condition known as flea allergy dermatitis. These unfortunate pets have an extreme response to even a single flea bite.

Often worse at the base of the tail, common symptoms of flea allergies include itchy skin, hair loss, self-trauma, and secondary skin infections. Treatment involves managing any skin infections, soothing itchy skin, treating the home environment for fleas (yes, part of the flea life cycle takes place in your house), and using flea prevention on all pets in the household for at least three months.

Food Allergies

Dogs and cats may develop allergies to the protein source in their diet (such as chicken, beef, fish, etc.), even if they have been eating the same diet for years.

Along with itchy skin, they may also show gastrointestinal signs, such as vomiting and diarrhea. A diet trial with a new or hydrolyzed protein is needed to diagnose and treat food allergies.

Environmental Allergies

Pollen, dust, or even other animals (or people!) can trigger environmental allergies, known as atopy. These allergies may have a seasonal pattern. If you wish to know what your pet is allergic to or treat them with allergy injections, a blood and/or skin test can be performed. There are also many medications that can help control the symptoms of allergies and decrease the frequency of flare-ups.

2. External Parasites

Parasites living on or in your pet’s skin and fur are another common cause of skin issues, leading to itchy skin, infection, and hair loss. In some cases, they can also transmit other diseases to both pets and human family members.

The best way to prevent external parasites is to use a broad-spectrum preventative product year-round. Since there are many product options on the market, ask your vet which preventative they would recommend for your pet.


Flea infestations can lead to severe itching and scratching, resulting in skin irritation and secondary skin infections. Some pets develop an allergic reaction to flea saliva, which can cause intense itching, discomfort, and scratching — a vicious cycle that can lead to more severe skin damage.

Closeup of parasite on dog's skin (Closeup of parasite on dog's skin)


Ticks can cause direct irritation and inflammation at the site of attachment, as well as transmit other diseases, such as Lyme.

Mange (Mites)

Demodex is a common form of mite that often leads to hair loss, scaling, and secondary bacterial infections. Demodex mites live in hair follicles and are usually not problematic unless a pet's immune system is compromised or immature, as in the case of young animals or those with other underlying diseases.

Scabies is another form of mange, which is highly contagious and causes intense itching. The mites burrow into the skin, leading to irritation, inflammation, hair loss, severe scratching, crusting, and secondary infections. Scabies can be spread to people as well as other animals.

Both types of mites are diagnosed with a skin scraping and treated with oral and topical medications.

3. Infections

Skin infection, known as pyoderma, can occur for many reasons and has many different appearances depending on the type, cause, and location of the infection. Skin infections can be caused by bacteria, yeast, or a combination of organisms, which can easily colonize damaged skin.

Most often, skin infections are associated with an underlying cause, such as allergies or external parasites. They are generally treated with a combination of topical and oral medications, such as antibiotics and antifungals. Some pets will recover from a skin infection and never get another! However, in many cases, skin infections will recur until the underlying condition is diagnosed and managed.

Cat with skin infection above eye getting treated by vet (Cat with skin infection)

Some common terminology you might hear from your vet includes:

  • Superficial pyoderma — The most common type of skin infection, affecting the upper layers of the skin and hair follicles
  • Folliculitis — Inflammation of the hair follicles
  • Moist or pyotraumatic dermatitis — The dreaded “hot spots”
  • Deep pyoderma — A more severe infection of deeper layers of the skin leading to pain, crusting, and oozing of blood and pus
  • Ringworm — Not a worm, but a contagious fungal infection
  • Otitis externa — Infection in the external ear canal
  • Pododermatitis — Infection of the paws

4. Systemic Disease

As the largest organ in the body, the skin and coat can often be a reflection of overall health. Systemic diseases in dogs and cats can often manifest as skin problems.

Conditions like hormonal imbalances, immune disorders, metabolic diseases, and organ dysfunctions can all lead to various skin symptoms, such as hair loss, changes in skin texture or color, itchiness, and the development of rashes or lesions. They may also be accompanied by symptoms of the underlying disease.

  • Hypothyroidism — This condition involves insufficient thyroid hormone production, which has a key impact on metabolism. Skin symptoms include hair loss, dryness, and increased susceptibility to skin and ear infections. Other signs include weight gain, lethargy, and cold intolerance. Hypothyroidism is more common in dogs, while hyperthyroidism is more common in cats.
  • Cushing’s Disease — Characterized by excessive cortisol (stress hormone) production, Cushing’s Disease causes changes to the skin such as hair loss, calcinosis cutis (hard calcium deposits), and infections. Additional symptoms include increased thirst and urination, and a pot-bellied appearance.
  • Immune-mediated disease — This group of conditions occurs when the immune system attacks the body's own cells, leading to symptoms like skin ulcers and depigmentation, especially around the nose and eyes. Diseases such as lupus, which can cause severe skin issues alongside joint pain and systemic illness, are common examples.
  • Cancer — Various forms of cancer can affect the skin directly (such as skin tumors) or indirectly (through systemic effects), causing lesions, ulcers, or abnormal growths on the skin. These signs often accompany weight loss, lethargy, and loss of appetite.
  • Liver disease — Hepatocutaneous Syndrome is a rare but severe liver condition that specifically impacts the skin. It's associated with chronic liver dysfunction, leading to skin lesions, ulcers, and crusting.
  • Feline eosinophilic granuloma complex — A grouping of inflammatory skin conditions in cats.

5. Lumps and Bumps

Lumps and bumps are extremely common in dogs and cats. They can occur beneath or on top of the skin, and range from benign (cysts, warts, fatty masses) to more serious conditions like abscesses (pockets of infection especially common in cats) or cancerous tumors.

Cat on the sidewalk with mouth open and scratching their neck area (Cat scratching neck)

Early detection plays a key role in managing potential health problems. It's crucial to monitor any new growths on your pet, and any changes in their existing lumps and bumps. Alert your vet so that they can take a look — however, keep in mind that many types of lumps and bumps appear similar. In most cases, your vet will recommend collecting a sample for evaluation. Treatment ranges from monitoring to antibiotics to surgical removal.

Thanks for reading Introduction to Pet Dermatology 101: Common Skin Conditions! In Part 2 of this series, we’ll look at how to manage common skin issues among pets.

Previous article Management of Common Skin Issues in Dogs and Cats: Pet Dermatology 102
Next article Cat Shedding 101: From Hairball Highway to Fur-Free (Or Close)

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