This information is provided by Provet for educational purposes only.

You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

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Atopy, also called atopic dermatitis, or allergic inhalant dermatitis is an allergic disorder to environmental factors that are inhaled, or sometimes absorbed across the skin, or swallowed..


Dogs that develop atopy are thought to have an inherited predisposition to develop IgE antibodies, and/or IgG antibodies,  to environmental factors - called allergens. Affected animals develop a Type I hypersensitivity reaction. However, the full, complex aetiopathogenesis of this condition in animals has still to be determined. It has been suggested that dogs are most susceptible to develop inhalant allergy if they are exposed to the allergen (eg pollen) within the first 4 months of life.

In cats the immunological cause has yet to be identified.

In humans atopic dermatitis is associated with several changes to the immune system including the following:

  • Poor cell-mediated immune responses
  • Overproduction of IgE by B-cells - although 20% of atopic humans have low IgE levels
  • T-lymphocyte activation
  • Overstimulation of Langerhans cells
  • Release of inflammatory mediators from eosinophils, mast cells and monocytes.
  • Abnormal biochemical responses in the skin

Breed Occurrence
Several breeds have been recognised as having a higher risk of developing the disease including the following which are reported in the literature :

  • Beaucerons
  • Beagles
  • Belgian Tervurens
  • Boston Terriers
  • Boxers
  • Cairn Terriers
  • Chinese SharPeis
  • Cocker Spaniels
  • Dalmatians
  • English Bulldogs
  • English Setters
  • German Shepherd Dogs
  • Golden Retrievers
  • Irish Setters
  • Labrador Retrievers
  • Lhasa Apsos
  • Miniature Schnauzers
  • Newfoundlands
  • Pugs
  • Scottish Terriers
  • Shih Tzus
  • Springer Spaniels
  • West Highland White Terriers
  • Wire-haired Fox Terriers

Clinical signs usually occur in dogs 6 mths - 7 years of age, with most occurring between 1-3 years of age and they consist of :

  • Itchiness (pruritus) - resulting in scratching, biting or rubbing
  • Reddening of the skin
  • Hair loss (alopecia)
  • Sites usually involved include:
    • The pinnae of the ears - and chronic otitis externa is a common complication
    • The face - around the eyes, sometimes the lips
    • The underside (ventrum) of the body
    • Under tail - the perineum
    • Under the front leg (the axillae)
    • Between the toes - cysts

In cats signs usually occur between 6 mths - 2 years of age and include :

  • Itchiness (pruritus)
  • Hairloss (alopecia)
  • Hairballs
  • Self-trauma - biting excessive grooming, broken hairs
  • Sites affected include the face, pinnae of the ears and neck.

In addition cats with atopy may also have other skin lesions including :

  • Eosinophilic complex lesions (red plaques)
  • Miliary dermatitis


  • Sneezing and coughing - in some cases
  • Many other signs

Atopy is more difficult to diagnose in cats than dogs because of the wide variety of signs reported.

Signs may be seasonal (eg pollen allergies) or non-seasonal (eg allergies to household products or house dust mites). In cats most (90%+) of cases are non-seasonal. 

If there is self-trauma the skin may be broken and secondary infection may occur:

  • Organisms involved include Staphylococcus intermedius or Malassezia pachydermatis
  • Spots may result - firm swelling (papules) or pus-filled swelling (pustules)
  • Crusts may form
  • Patchy hair loss may occur with scale around the bald spot

If the condition has been present for some time secondary changes may occur in the skin, including :

  • Thickening
  • Black pigmentation

Complications include :

  • Secondary infections
  • Chronic otitis externa


Diagnosis is often based upon the presenting history and signs

Confirmation of the diagnosis can be made sometimes by:

1. Intradermal skin testing - challenging the skin by injecting into it common allergens. Care has to be taken not to over-interpret positive reactions. For example, many dogs have been exposed to housedust mite in their environment  and so they may show a positive reaction when injected with housedust mite allergen. However, this does not necessarily mean that allergy to housedust mite is the cause of an episode of acute dermatitis. Positive dogs often react to several allergens eg housedust mite and pollens.

False negatives may occur if :

2. Serology testing - these tests (RAST, ELISA, Immunoenzyme assays) measure allergen-specific IgE in blood . However, false positives are common with many normal dogs showing positives, so interpretation of results can be difficult and many veterinary dermatologists consider reliance on these tests for diagnosis to be controversial.

3. Basophil degranulation test is reported to be a useful test but it is confined to research laboratories at this time.

NB Skin biopsies are NOT diagnostic for atopy in cats or dogs.


Apart from avoiding contact with known allergens - which is possible in some cases:

  • Removing houseplants from the animals environment
  • Hoovering up house dust
  • Ban smoking in rooms occupied by the pet

There are basically 2 forms of treatment:

  • Hyposensitisation to reduce the immune reaction to allergens in the environment, and 
  • Treatment to relieve the signs of the disease

1. Hyposensitisation (also called immunotherapy)

Many (50%+) dogs can be hyposensitised by giving increasing doses of allergens (antigens) that the animal is sensitive to by injection. This theoretically results in the production of circulating IgM antibodies in the blood which bind to the environmental allergens and blocks them before they stimulate local IgE or IgG antibody production in the skin. In addition, the animal becomes tolerant to the allergen.

2. Symptomatic treatment

Most dogs with atopy (c90%) can be controlled , although treatment may need to be given for life. Some of the drugs that are used may have undesirable side-effects so the choice of drug therapy must be based upon consideration of the individual animal. The clinical objective is to give therapy at as low a dose as possible, and as infrequently as possible to control the signs.

Drugs that are used include :

  • Corticosteroids - most widely used, but can have serious side-effects. 
    • Prednisone
    • Prednisolone
  • Antihistamines - effective at preventing the onset of pruritus  in some individuals, but not in others. Not so effective when pruritus is already present.
    • Amitriptyline
    • Chlorpheniramine
    • Clemastine
    • Diphenhydramine
    • Hydroxyzine
  • Non-steroidal antinflammatory drugs
  • Other drugs - few reports confirm that they are effective.
    • Orgotein
    • Tranquillizers
    • Barbiturates
    • Levamisole
  • Nutritional modification - essential fatty acid supplementation eg evening primrose oil (gamma-linolenic acid), omega3/6 mixtures..


A large number of atopic dogs (c80%) will go on to develop non-seasonal pruritus.

Long term problems

Chronic treatment with corticosteroids can lead to complications such as diabetes or liver disease

Last updated : March 2008