Allergies in Cats

short hair cat resting on a sofa

An allergy is an endogenous reaction against normally harmless substances (allergens or antigens) in which the body forms certain protective proteins known as antibodies. This antigen-antibody reaction can ultimately lead to several secondary reactions, which can trigger life-threatening situations along with harmless skin inflammations. In principle, all cat breeds can be affected by an exuberant immune reaction, which can occur spontaneously at any time.

To better understand how allergies and consecutive diseases develop in cats, the allergic responses can be divided into the following 4 types:

  1. Immediate type:
  • Generally occurs within a few seconds or minutes.
  • Is the most common type affecting cats.
  • Formation of IgE antibodies, which lead to a sharp increase of histamine in the body.
  • Example: allergic asthma.
  1. Cytotoxic type:
  • Starts within a few hours. 
  • Links between cell-bound antigens and endogenous antibodies (immunoglobin G, IgG) lead to the formation of immune complexes, which in turn lead to the destruction of somatic cells such as blood platelets (thrombocytes) or red blood cells (erythrocytes).
  1. Arthus or immune complex type:
  • Emerges within a few hours.
  • Also formation of immune complexes between antigens and antibodies, although this reaction is not only cell-bound and also occurs on freely mobile antigens.
  • Example: allergic vascular inflammations (vasculitis)
  1. Delayed type:
  • Only emerges after several hours or days.
  • Certain immune cells (T-lymphocytes) attract other immune cells to the allergen and trigger inflammation there.
  • Example: transplant rejection following an operation.

Environmental allergy (atopy)

Like us humans, cats can also develop allergies to diverse environmental allergens like pollen or house dust. The latter usually causes a year-round allergic skin inflammation, whilst a pollen allergy is typically seasonal. Further examples of other airborne allergens are mould spores or fragrances, which can be found in cat litter.

Flea saliva allergy

Allergic reactions in cats are triggered particularly often by flea infestations, more precisely flea saliva. Affected cats typically show small inflammatory nodules on their back, which is known as miliary dermatitis. Increased licking due to severe itching can lead to the skin inflammation worsening through bacterial or fungal secondary infections.

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Food allergy

Along with flea saliva allergies, food allergies are also commonly observed in cats.

They can emerge spontaneously and lead to diarrhoea and vomiting, as well as itching. It’s important to differentiate a food allergy from a food intolerance, since this is not triggered by immune-mediated hypersensitivity.

Eosinophilic granulocyte complex (EGC) in cats

There is not yet any exact known cause for this allergic disease specific to cats. However, the assumption is that a flea infestation can be a trigger. The disease leads to a strong defensive reaction from the immune system, which leads to inflammatory nodules (eosinophilic granuloma) and at times severe pain in the mouth area in particular. Along with inflammation of the mucous membranes, inflammation can also occur in other skin regions like the head or inner thigh.

Symptoms of allergies in cats

The clinical picture of allergy in cats is very variable and can include the following symptoms:

  • Severe itching: scratching and rubbing against objects
  • Hair loss (alopaecia)
  • Gastrointestinal complaints: nausea, vomiting, diarrhoea
  • Bacterial secondary infections: skin and other organ inflammations
  • Allergic asthma and anaphylactic shock: sudden danger to life due to respiratory difficulties


You should see your vet if your cat shows signs of an allergy. The vet can limit the allergens through exclusion diagnostics and prevent symptoms from worsening. For this purpose, the vet asks during the owner interview (anamnesis) for important indications to detect possible allergens. For instance, a flea saliva allergy is very unlikely if the cat has received an effective flea treatment throughout the entire year.

In contrast, a seasonal accumulation of allergic phases is a sign of a pollen allergy.

The general clinical examination takes place after the owner interview, which gives information on the cat’s general state of health. For instance, breathing, pulse and heart rate are measured, as well as the inner body temperature with a rectal thermometer.

The special examination can commence if the cat doesn’t show any drastic changes to its vital parameters.

The objective of the special examination is to establish the cause of the allergy through specific tests. For instance, a food allergy is diagnosed by what is known as an elimination diet, an abrupt, long-term change in food. If the cat’s symptoms improve, a positive result can be expected. However, the cat can be fed its old food once again in order to confirm the suspicion. If the client shows clinical indications again, a food allergy is highly probable.

If the allergens cannot be detected by exclusion diagnostics, there are still more specialised tests available to vets like skin tests (intradermal tests) or blood tests (serum tests). They can specifically detect allergens, although unfortunately the results are not always reliable.


Treating an allergy in cats is based on the cause and extent of the clinical picture.

The following treatment methods may be necessary in order to increase the affected cat’s quality of life or even possibility of survival:

  • Anti-allergy medication (e.g. anti-histamines)
  • Immunosuppressants (e.g. cortisone or Atopica)
  • Anti-inflammatory shampoos or spot-ons
  • Secondary infections: antibiotics (following a resistance test) or antimycotics
  • Desensitisation (hyposensitisation) through lifelong administration of individually manufactured allergens


Cat allergies are very common and are generally mild. However, in a few cases there can be severe anaphylactic shocks, which can be fatal due to shortness of breath. Hence, it is very important to prevent further allergic phases.


Allergies can emerge at any time. However, the following preventing measures can be heeded to reduce the risk of an allergy developing or other allergic steps:

  • Avoiding contact with known allergens
  • Regular flea prevention (e.g. spot-ons or collars)
  • Desensitisation
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