Like humans, dogs and cats may suffer from allergy (hypersensitivity) to various elements, called allergens: flea bites (allergic dermatitis to flea bites), pollen or mites (atopic dermatitis), food products (hypersensitivity or food allergy or atopy).
In animals, these allergies manifest primarily at the skin level and mainly cause itching.

Thus, the affected animal may experience a strong impact on its everyday comfort. Therefore, it is essential to identify the cause of itching. The treatment to be implemented depends on the allergen.

Whatever the nature of the allergen, allergic dermatitis is a chronic disease that will affect the animal throughout its life. Even though it is impossible as of today to completely cure the condition, there are actions and treatments to enhance the animal’s everyday comfort.

To take care of these skin disorders and achieve better results, it is vitally important to involve the owner and ensure they understand the nature of the disease.



Atopic dermatitis is allergy to the elements in the environment (pollen, mites, mould, etc.) or to food products. It manifests by itching and skin lesions in dogs and cats. The most common allergens are pollen and mites in the dust, which can explain the exacerbation of symptoms during certain times of the year. Weakened skin predisposes an animal to this disease. Allergens can enter the body through the skin, respiration or with food. They stimulate an abnormal response from the immune system at the skin level, causing inflammation and itching.

In dogs, this is the second cause of itching. In cats, the concept of atopic or allergic dermatitis is not known as well.

The diagnosis of atopic dermatitis is a strict and systematic process. First of all, it is advisable to exclude other causes of itching: parasitic infestations, bacterial or fungal infections.

Then it is necessary to use skin and/or blood tests to identify the allergens that cause hypersensitivity. Skin tests are the standard method in dogs but are harder to use on cats.


Atopic dermatitis is a chronic, incurable disease that cannot be eradicated in an animal. However, there are several measures that can be taken to enhance its life quality. If allergens are identified, it is possible to begin desensitisation or hyposensitisation.

Moreover, it is often necessary to soothe the itching and skin inflammation. The veterinarian can decide to administer anti-inflammatory agents systemically or locally, as well as antipruritic or immunomodulatory agents. A combination of these treatments may be necessary. It is also important to moisturise the skin and to supply lipids locally or systemically in order to enhance the level of skin defences (to fight the absorption of allergens by the skin).

Finally, anti-infection treatments must be used if there are any superinfections.


Some breeds of dogs are predisposed to atopic dermatitis: Beauceron, English bulldog, French bulldog, Boxer, German Berger, Cairn terrier, Chihuahua, Labrador, Setter, Shar-Pei, Yorkshire Terrier, West Highland white terrier, Cocker and golden retriever. The most commonly affected areas are the face and the ends of the paws. Other areas may be affected, depending on the breed and on how long the disease has been progressing.3 At first, there are no lesions, but the animal scratching and licking itself as well as chronic inflammation will bring them about (abrasions, hair loss, densification and change in skin colour).

No cat breeds that may be predisposed to atopic dermatitis have been identified so far. In this species, pathologies can take several forms 4:


Itching localised on the face and neck,

Inflammation of the outer ear (external otitis),

Hair loss over the entire body, either symmetrical or local (often due to intense licking of the affected areas) with hair abrasion,

Plaque rouge surélevée et dépilée, parfois suintante, sur n’importe quel endroit du corps,

Elevated red plaques with hair on them gone, sometimes with discharge, anywhere on the body Miliary dermatitis (inflammation the skin that manifests by a sand-like sensation from the animal’s hair when stroking it).

As cats have sharp claws and a rough tongue, they can injure themselves very severely while scratching or licking themselves because of the itching.



Fleas are insects of several millimetres in size which wander about in pets’ hair and feed on their blood by biting them. When biting, the flea injects its saliva into the skin and blood of its host, which can cause local inflammation. The more flea bites, the stronger the itching sensation. Due to the contact with the saliva of the flees, the immune system of some animals can develop an exaggerated response. This can make the animal suffer from very severe, sometimes painful itching even from a single flea bite.

Thus, the animal suffers from dermatitis (inflammation of the skin) due to allergy to flea bites. This is the most common skin disease in dogs1 and one of the most common skin diseases in cats2.

The diagnosis is based on several components:

The owner’s practices in the prevention of parasites,

Localisation of lesions,

Presence of fleas and/or their droppings in the animal’s hair,

The animal’s surroundings and way of life.


Whatever their breed, all dogs and cats are susceptible to developing an allergy to flea bites at some point in their life. The most commonly affected areas are the lower back and base of the tail, as well as and the inner side and back of the thighs. Yet itching often develops on other areas of the body, in particular if the infestation is heavy.


First and foremost, the management of allergic dermatitis consists of preventing flea bites. It is necessary to completely eradicate fleas in the affected animal and in its surroundings. This should eliminate all fleas that could bite it and will avoid the repeat infestation of the animal and its living environment.1,2 Just a single flea bite is enough to bring the symptoms back, which is why the veterinarian’s recommendations must be strictly followed.



Dogs and cats may develop an allergy (hypersensitivity) to one or more components of their food. Developing food hypersensitivity requires a prior exposure to the substance (allergen) in question. Thus, the disease is often caused by eating one food product for a long time.


Food allergens are the proteins or additives, most commonly beef proteins or dairy products. There are often several allergens causing trouble in a single animal.


Food hypersensitivity is the third most common allergy with skin manifestation in dogs.6 In cats, it accounts for 11% of cases of miliary dermatitis (inflammation the skin that manifests by a sand-like sensation from the animal’s hair when stroking it).


In cases of food allergy, digestive symptoms are rare in dogs, with skin symptoms prevailing. Itching caused by food hypersensitivity may be localised on the face, ears, paws, in the axillary, inguinal or perineal region, or be spread over the entire body.


The symptoms in cats are different:

Digestive (vomiting, diarrhoea),

Localised itching, in particular on the face and neck (cervico-facial pruritus) or over the entire body,

Miliary dermatitis,

Elevated red plaques with hair gone, sometimes with discharge, anywhere on the body (eosinophilic granuloma complex-associated lesions).


Some breeds of dogs are at greater risk of developing food allergy. A few examples are Boxer, Cocker, Dalmatian, German Berger, Lhassa Apso, Shar-Pei and West Highland white terrier. As to cats, two breeds have been identified as predisposed: Siamese and Birman.

Animals affected with food hypersensitivity are often also allergic to fleas and suffer from atopy.


The treatment consists of avoiding the food in question. Occasionally, it may be necessary to give the animal anti-inflammatory, anti-pruritic and/or immunomodulatory agents during itching crises.


After making sure that there is no parasitic infestation or skin infection in the affected animal, an elimination diet should be implemented. This consists of feeding the animal for a certain time only with a ‘new’ food product whose components are unknown to it. If the itching disappears, a stepwise reintroduction of the ‘previous’ food products will allow to exactly identify the one or ones at cause.