Dog - Allergies or Hypersensitivities - Is there any difference?

My dog has scratched on and off all his life.  Depending on the vet who examines him I am either told that he has a flea allergy or a flea hypersensitivity.  I have seldom seen any fleas.  Can you explain this?

Allergies are common in dogs.  Canine allergic skin disease is a difficult and frustrating problem for vets.  More accurately the condition should be called a hypersensitivity reaction, thus the terms flea allergy and flea hypersensitivity are synonymous (mean the same thing).

These reactions occur when the immune system 'overreacts' to a foreign substance (the allergen or antigen).  This then leads to tissue damage.  Most commonly the reaction results in pruritus (itching).  This may be confined to one area (localised) or all over the body (generalised).  If the allergen is inhaled (e.g. pollen) the result may be coughing, sneezing and/or wheezing, rather like hay fever in people.  Certain food constituents can act as allergens and can cause signs such as diarrhoea.  Certain substances coming into contact with the skin can result in contact allergies.

I have had two related West Highland White Terriers.  Both of them have had allergic skin disease.  Are they born with it?

Animals are not born with allergies but develop them after repeated exposure to an allergen.  For example a dog may develop a food allergy dermatitis having been fed the same diet for many years.

Some breeds appear to be more prone than others and inheritance may play a part.

Can the condition be cured?

Depending on the cause of the hypersensitivity effective treatments are available.  Unfortunately dogs may become allergic to more than one substance and may also develop new allergies after previous ones have been identified and controlled.

Therefore, am I right to assume there are different types of allergies or hypersensitivities?

Yes, there are at least five known types of allergies in the dog.  These are:-

1. contact
2. flea
3. food
4. bacterial
5. atopy (also known as atopic disease, atopic dermatitis or allergic dermatitis)

Each have some common features and also there are some unique features.  All of them result in pruritus or itching.

How do I know if my dog has an allergy or hypersensitivity?

Irrespective of the allergen the most common reaction affects the skin.  There is intense pruritus (itching) so the dog tends to want to continually chew, lick or scratch.  This can cause hair loss or lead to open sores or scabs which can become secondarily infected leading to a condition called pyoderma.

What does treatment involve?

Initially it is important to try to establish the cause, i.e. the allergen.  This may involve referring your dog to a veterinary dermatologist (skin specialist).  Sometimes diagnosis takes a while, for example with food allergies special exclusion diets have to be fed to establish which particular foodstuff is causing the problem.  Recently special blood tests have been developed which help with diagnosis.  Once the cause has been established treatment can then begin.

My dog is supposed to have a flea hypersensitivity but I have never caught a flea on him.  I find the diagnosis difficult to believe.

Flea hypersensitivity is due to the dog's reaction to the chemicals contained in the flea's saliva when it bites the dog.  Once the hypersensitivity has developed all that is necessary is a single bite from a passing flea to start the reaction.  Thus you may never see that flea.  Our handout on Flea allergy dermatitis explains this more fully.