Dermatology / Allergy - Related Articles

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Most Common Allergic Skin Diseases


Atopy is the term used to describe allergic skin and ear disease to normally harmless substances in the environment. These substances are called allergens and include pollens (trees, weeds and grasses), molds, house dust mites, danders and dusts. Atopy is like “hayfever of the skin”. Patients with atopy are typically itchy (scratching, biting, chewing, licking, rubbing, etc), exhibit hair loss, and are prone to developing secondary yeast and/or bacterial infections of the skin and/or ears. Signs may be seasonal or non-seasonal. To help patients with atopy, symptomatic therapies with antihistamines, fatty acids, etc. may be used. In addition, allergy testing and immunotherapy (allergy shots) are often helpful in relieving your pet’s allergy signs; this therapy is also quite safe. Two types of allergy testing are currently available; they are intradermal allergy testing (skin testing) and serum (blood) allergy testing. Most dermatologists feel that intradermal allergy testing is the most reliable allergy test available.

Food Allergy

Food allergy is an allergy to one or more ingredients within your pet’s diet. Food allergy typically causes non seasonal itchiness (scratching, biting, chewing, licking, rubbing, etc.). Your pet may also exhibit hair loss and may be prone to developing secondary yeast and/or bacterial infections of the skin. Chronic ear infections and anal gland infections may also be seen. Some pets may also show gastrointestinal signs such as vomiting, diarrhea, burping, flatulence (gas) and/or have a sensitive stomach. Blood and skin tests are available for food allergy diagnosis, however these tests are considered very inaccurate and are not recommended by most veterinary dermatologists/allergists. A strict food elimination diet trial is the best “test” for food allergy diagnosis.

Flea Allergy

Flea allergy can affect both dogs and cats. Flea allergy results from an allergic reaction to the flea’s saliva. Fleas and/or flea dirt may or may not be seen on your pet or in your home. Dogs will typically bite or chew at the rump, belly, tail area and/or hind legs. This often results in hair loss. Papules (red bumps) and crusts (scabs) may be seen. Cats may also display signs of chewing or licking at the rump area, however they may also have tiny crusts scattered throughout their body, lick their hair out or have ulcers. Flea allergy is best treated with flea control. Today, many safe and very effective flea control products are available by prescription. For the most part, the over-the-counter flea control products are not as effective or safe as those available by prescription.

Autoimmune Skin Diseases

Autoimmune (immune-mediated) skin diseases are a group of disorders where the immune system “attacks” the skin causing various skin lesions including loss of pigment, crusts (scabs), erosions, ulcers, hair loss, etc.

Discoid Lupus Erythematosus (DLE)

DLE is the second most common immune-mediate skin disease in the dog. DLE is considered to be a benign variant of systemic lupus erythematosus (SLE). DLE most commonly affects the nasal planum (nose) and results in loss of pigmentation, redness, crusts, bleeding, erosions and ulcers (deep sores). The lips, ears, eyelids, genitalia and feet may be affected. Tissue loss and scaring can occur. Sunlight may exacerbate DLE. Definitive diagnosis requires tissue biopsies of the affected area(s). Many different therapies are available for patients with DLE and often depend on the severity of the disease.

Systemic Lupus Erythematosus (SLE)

SLE is a multi-system autoimmune disease characterized by the formation of autoantibodies against various self-antigens and immune complexes. SLE can affect many different body organs, including the skin. Some of the more common clinical signs include fevers, joint pain, skin lesions, enlarged lymph nodes, enlarged abdominal organs, kidney problems, anemia, low platelet counts, lethargy, poor appetite. Affected patients may display only a few of these signs or many of these signs. SLE can be tricky to diagnose and challenging to treat.

Pemphigus Foliaceus (PF)

PF results from the immune system “attacking” the adhesions between the skin cells. This results in several skin signs including pustules, scale, crusts, red skin, erosions, erosions and hair loss. Any part of the pet’s skin may be affected. The footpads and mucous membranes are also sometimes affected. The PF lesions may be uncomfortable, itchy and/or painful. Sometimes pets with PF may be lethargic or depressed and/or have a fever and/or a poor appetite. Bacterial skin infections may be present concurrently. Definitive diagnosis requires tissue biopsies of the affected area(s). Therapies for patients with PF often often involve suppressing or modulating the immune system. The best therapies for your pet will be determined by our veterinary dermatologist.

Hormonal Endocrine Skin Diseases

Below are some of the most common hormonal (glandular) diseases that can involve your pet’s skin.


Hypothyroidism is a hormonal condition caused by an inadequate production of thyroid hormone in your pet’s body. Reduced levels of thyroid hormone in the body result in a generalized decrease in metabolic activity. Hypothyroidism is much more common in the dog than in the cat; in fact this is quite rare in the cat. Dogs may exhibit hair loss, a dry, dull haircoat, dandruff, hyperpigmented skin, excessive shedding, weight gain, and lethargy as well as other some other signs. Also, dogs with hypothyroidism may be more prone to recurrent skin and/or ear infections. Hypothyroidism is most commonly diagnosed by blood tests after examination and possibly ruling in or out other possible causes of your pet’s signs/problems. Lifelong thyroid hormone supplementation is the treatment for hypothyroidism.

Cushings Syndrome (Hyperadrenocorticism)

Cushings is a hormonal disorder caused by an overproduction of natural steroids (cortisol) by the body. This results in various clinical signs. Clinical signs seen in dogs include hair loss, blackheads, hyperpigmented skin, lethargy, muscle atrophy, obesity, increased thirst and urination, excessive panting, pot-bellied appearance, skin infections. A big liver and/or small testicles may also be noted. Cats with Cushings may have very fragile skin (which may tear), thin skin, hairloss and be lethargic. Pet’s with Cushings may display one or all of these signs. Diagnosis can sometimes be challenging requiring several different tests. Treatment is aimed at reducing the amount of cortisol in the body.

Infectious Skin Diseases


A bacterial infection on the skin (esp. the hair follicles). This usually involves the torso, but may affect the chin, bridge of the nose, elbows, hocks, and feet. Visible signs are pustules, crusts, scaling, hair loss, and darkened skin. Pyoderma lesions can sometimes be variably itchy. Pyoderma is a common sequela to allergies and/or hormonal problems. Antibiotic therapy is the treatment of choice. Medicated shampoos compliment antibiotic therapy.

Dermatophytosis (Ringworm)

A fungal infection affecting hair follicles, hair, nails and top layers of the skin. Typically hairloss and scaley skin are seen, however clinical signs can be highly variable. This can be contagious to people and other animals.

Malassezia (Yeast) Dermatitis

Yeast dermatitis is a skin infection caused by yeast, esp. Malassezia pachydermatis. This is more common in the dog than in the cat. Yeast dermatitis is often secondary to allergic skin diseases, and sometimes to keratinization or hormonal skin problems. Clinical signs include red, itchy skin, hairloss, greasy malodorous skin, hyperpigmented skin, etc. The yeast can often be found via cytological examination of the skin with the aid of a microscope.

Parasitic Skin Diseases

Demodicosis (Demodecitc mange)

Skin disease caused by the Demodex mite. This appears to be more common in the dog versus the cat. Most canine demodectic skin diseases are caused by the hair follicle mite, Demodex canis. Demodicosis is seen most commonly in puppies. Clinical signs include hairless patches that may be red and scaly or hyperpigmented. Most often affects the face, but can be found on the body and legs. Dogs may or may not be itchy. Bacterial infections may be present. Demodicosis in cats is less common; hair loss and/or itchiness (esp. licking and scratching) are the most common signs seen. Diagnosis is most commonly made by finding the mites on deep skin scrapings visualized microscopically.

Scabies (Sarcoptic mange)

Scabies is caused by infestation with the Sarcoptes scabiei var. canis mite which affects dogs and very rarely cats. Scabies is a contagious parasitic skin disease (esp. contagious from dog to dog and dog to people). Patients are extremely itchy. In addition, hair loss and papules (red bumps) on the elbows, hocks, ear margins, abdomen and chest may be seen. Bacterial skin infections may also be present. Diagnosis may be made by finding the mites (with the aid of a microscope) on skin scrapings, however these mites are often extremely difficult to find on scrapings. Some say scrapings may only be positive in 20% of the cases.

Cheyletiellosis (Walking Dandruff)

Cheyletiellosis is a contagious skin disease of dogs, cats and rabbits and is caused by infestation with mites of the Cheyletiella species. This mite is also contagious to humans. Clinical signs are variable and include dandruff or excessive grooming. Itchiness may be mild, moderate to severe or nonexistent. Diagnosis is most often made with skin scrapings, flea combing and/or acetate tape preparations and then finding the mite under the microscope.

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