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It is not unusual for a dog or cat to scratch or lick during the day. However, done too much, these scrapings are defined as pruritus and are considered abnormal. Rapidly, areas of hair loss, or alopecia, are discovered as well as the appearance of red and oozing areas. The most common causes of pruritus and dermatitis are these three groups of dermatitis:

  • Allergic: initially caused by parasite bites and/or topical (contact) allergies
    or food allergies.
  • Infectious: caused by bacteria and/or yeast (or fungi).
  • Parasitic: caused by parasitic insects and/or arachnids.

Allergic Dermatitis

Very common in dogs and cats. Their diagnosis and treatment are often difficult because these diseases all have similar symptoms. Two or even three allergic dermatitis can inconvenience the same animal thus complicating the differential analysis of the diagnosis. Moreover, if one waits too long before having his companion treated, these allergic dermatitis tends to be complicated.

Flea Allergy Dermatitis (FAD)

Flea infestation is a common phenomenon in our regions. However, in some hypersensitive individuals, it can cause pruritus and major lesions. Fleas, when biting for food, inject saliva and anticoagulant substances into the skin. It is through these oral allergens that the animal develops an allergy to flea bites. For individuals with FAD, a small amount of injected flea saliva is sufficient to trigger and maintain lesions. It is therefore possible to note a FAD without the presence of fleas on the animal. The symptoms are: alopecia due to scraping, crusts, erythema and papules.


Atopic Dermatitis and Contact Dermatitis

This type of dermatitis occurs in animals that are hypersensitive to certain allergens found in the environment such as: pollen, house dust mites, moulds, tissues, chemicals in fabrics, etc. These allergens are found in their system by the respiratory route or by the skin. In general, scratching occurs before the onset of symptoms. Generalized and localized pruritus is observed. The resultant can be; otitis, conjunctivitis or asthma in cats. Here in our regions, we observe contact allergies sucking insect bites (black flies, mosquitoes, deer flies and horseflies). We will then note erythema and papules in the regions of the belly, armpits and around the eyes. It is recommended to keep our animals indoors during big flies. Thus, we avoid the anaphylactic shock that occurs unfortunately too often when an animal is stung repeatedly.


Food Allergy

It is most often impossible to distinguish clinically food allergies and atopic dermatitis. However, the former is often linked to the presence of digestive disorders such as vomiting, flatulence and diarrhea. For the dog, the lesions are found at the extremities. In cats, the lesions will occur especially on the face and neck. In their case, the precursor symptoms are mainly diarrhea.


Infectious Dermatitis

Pruritus dermatitis is often infectious. The dog is more frequently affected than the cat of these affections. In the latter, they are sometimes associated with serious diseases. In dogs, they may be of unknown cause, but they are more often secondary to allergic dermatitis and more generally to any inflammatory state of the skin.


To malassezia
Photo courtesy:

Malassezia is a yeast affecting both dogs and cats. Symptoms include; pruritus, smell of old fat, redness, black skin and thickened resembling an elephant skin.


Pyoderma Bacterial Infections
In the dog these types of infections, caused by a staph, create pimples, scabs, or irritation of the choker, or worse, lesions in the form of escutcheon when they are very inflammatory. The pyoderma does not exist in cats because their skin is resistant to bacterial infections.


This painful infection is found in the dog with a dense undercoat in summer when it is hot and humid. Also known as “Hot-Spot” (HS) this dermatitis is a superficial bacterial infection of the skin that appears acute and develops rapidly following a traumatic skin. This initial trauma associated with localized pain is exacerbated by excessive licking, biting or scraping. Then the bacteria in this area multiply suddenly because the skin’s barrier is no longer impervious to bacterial invasion. Auto-trauma occurs as a result of a parasitic sting, an allergy, moisture rash, a bacterial infection or a fungus. It is therefore essential to eliminate the cause (s) of the underlying itching, under penalty of frequent recurrences.


Observed especially in cats, some generalized forms of ringworm become itchy, but are rarely prone to sparse circular lesions. They appear, most often on the head, where there is an absence of hair. Ringworm is transmissible to all mammals, including humans. It is therefore a zoonosis. Some cats may carry ringworm—and contagious—without presenting the slightest lesion.








Left picture: lesion characteristic of ringworm. Right: Larger lesions on the back of a cat.
Photos courtesy

Parasitic Dermatitis

Several parasites are vectors of cutaneous affections accompanied by important itching. Many are mites and some of the insects. It is therefore important to check their presence in case of pruritus and treat all animals in the house and sometimes even the latter.


The Cheyletiellose, a mite, lives on the skin and feeds on skin debris settles on the back of the animal (dog or cat) where large dandruff forms. Pruritus is usually mild. In dogs, dwarf breeds are predisposed and in cats, this dermatosis is often encountered in Persians.

Photo of a young puppy with a demodex infestation

The demodex is another mite that lives and multiplies in hair follicles, but rarely causes an itch. However, it is very inflammatory and is manifested by hair loss. It is seen more often in young animals and stressed animals.

Dog Scabies
Scabies remains a fairly common affection. The female of this mite lives in the skin and is the source of an aggressive and often uncontrollable scratching. Lesions that look like pointed pimples are present mainly on the belly as well as on the paws and the face.

Ear Mites
Ear mites are mites. Their presence is manifested by an abundant blackish earwax in the inner ear canal and by an important pruritus of the ears. The outer pavilion of these can be mangy and bleed by scratching by the animal.

Lice are biting insects specific to the species and are visible to the naked eye. They are found more often on weakened animals or on large-scale farms.

The flea is an insect that lives temporarily, in its adult state, on the dog. This parasite feeds and breeds on its host, but lives its other stages of development (eggs) exclusively (larvae and pupae) in the environment. In all forms, about 5% of fleas live on animals, while 95% are in the outdoor environment.

In conclusion, if your dog or cat is scratching or licking excessively and you notice skin lesions, consultation with the veterinarian is essential. By consulting from the beginning of the symptoms, an accurate and rapid diagnosis can be made as well as an effective treatment. Thus, you will avoid all complications and recurrences.

© Martine Lavallée B.A.A. and Animal Health Technician

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