Today, we know that the body can experience an allergic response to almost anything, including foods, drugs, and chemicals and your dog is no different than you are in that respect.

In your dog, two systems are primarily affected by allergies: the skin and the gastrointestinal systems. The indicators of allergy are frequently mistaken for signs of other, often more common conditions. Itchy skin, and especially itchy ears, is commonly attributed to parasites, while food poisoning from scavenging is often erroneously thought to be the cause of either vomiting or diarrhea.

Most dog allergies are caused by allergens in the environment, with only about 15% caused primarily by food. The most common environmental causes are the house dust mite and, somewhat poetically, human dander. It is only since dogs were welcomed into our homes – and particularly into our bedrooms and beds – that they have experienced their greatest leap in the incidence of allergy!

Some dogs, particularly those with white coats, are especially prone to an allergic reaction to the chemicals injected by fleas when they bite; a single flea bite can lead to the dog's whole body flaring up. Fungal spores can also precipitate an allergic reaction.

Just as allergies tend to run in human families, there is also a breed disposition in dogs. Generally, ancient breeds, such as the Shar Pei and Japanese Akita are prone to skin allergies, while Golden Retrievers and Westies are susceptible to gastrointestional allergies.

At the same time that the incidence of allergy has increased (now affecting almost one in five dogs), numbers of immune-mediated disorders also appear to have risen. For example, Cocker Spaniels are particularly susceptible to hypothyroidism, where the immune system mistakenly decides that the thyroid gland in "foreign" and destroys it, leading ro medical and behavior problems cause by low thyroid hormone levels. Reports of immune-mediated disease have increased dramatically over the last few years, but this could simply be down to better diagnoses.

External parasite prevention, especially flea control, is high on the list of measures to reduce both the risk and the severity of allergic skin reactions. So too is routine shampooing. A terrier's rough coat, for example is adept at capturing two causes of allergy, namely mold spores and pollens, but washing can remove them. The essential fatty acids found in fish oil and linseed oil added to the daily diet may also be beneficial in reducing the allergic response. Any dog that suffers from chronic allergy – skin or gastrointestinal – should be fed a unique, changed diet, such as fish and potato, for at least six weeks, to determine whether food is a complicating factor.