Allergic skin disease can be caused by a wide variety of factors including parasites (fleas), environmental factors (grasses and pollens), or household allergens (dust or dust mites). It can, however, also be caused by a food allergy.

Approximately 1 in 5 dogs and cats with itchy skin will have a food allergy and it is important to rule this out in order to get to the bottom of a persistent skin problem.

For cats, the most common source of allergens are beef, fish and chicken, and for dogs it is beef, dairy and chicken. Diagnosing a food allergy is difficult – no commercially available laboratory test will reliably diagnose a food allergy in dogs and cats, so the best way to reach a diagnosis is by an elimination diet trial.

Two types of elimination diet

Two options exist – the home prepared novel protein diet; this could be formulated using unusual protein sources such as venison, rabbit, lamb, etc. However, care should be taken to make sure these are balanced, ideally containing vegetables and grains which are an unlikely source of allergens.

The second option is the commercial hypo-allergenic diet; the ones preferred by veterinary dermatologists generally contain hydrolysed proteins. Hydrolysis reduces the size of protein molecules to such a small size that they cannot trigger an immune response.

These diets tend to be carefully manufactured so cross contamination with other protein sources is unlikely. They are regarded as a more reliable diet for elimination trials than a generic ‘hypoallergenic’ pet food that may use a mixture of proteins, not all of which may be mentioned on the label! Hills Prescription Diet z/d, Royal Canin Hypoallergenic/Anallergenic and Purina HA Hypoallergenic are all examples of hydro-lysed protein diets.

The elimination diet should be persevered with for at least two months and during that time all other dog treats, tidbits and human leftovers should be avoided. Individual proteins can then be added back into the diet once the skin itch has resolved to determine which was the offending allergen. Although not the most common cause of skin disease in dogs and cats, food allergies play their part and can be relatively easily avoided once diagnosed.