Dr Liesel van der Merwe is a small animal medicine specialist. Send her your questions: This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Dr Liesel van der Merwe

Scratching, licking and grooming are normal in dogs and cats. In some animals, however, it is excessive and due to an underlying condition which is causing itchy skin (pruritis). This could be a bacterial skin infection with pimples and round flaky lesions, parasites such as mites (demodex and sarcoptic mange) and allergic skin disease.

Skin allergies are common in dogs and the cause can be divided into contact allergy (<10%), food allergy (30%) and atopy (60%). Animals with food allergies will also often have gastrointestinal symptoms.

Atopy occurs when the skin is exposed to environmental allergens such as pollen, mould spores, insect saliva (fleas), house dust mites and feather dander. As these particles settle on the skin they penetrate the superficial layer to the surveillance cells beneath the top layer.

These cells then identify and pick up on the membrane markers of the allergens and take this information to the immune system. Animals which are allergic do not have “tolerance” for these antigenic markers and their immune system will respond and cause inflammation, which manifests as itching.

Atopy and food allergy generally becomes apparent only after six months of age. Initially the signs may be mild but they will progress with age. Atopy is often seasonal. The distribution of the lesions is usually typical with food allergy and atopy affecting paws, ears, eyes, face and inner legs.

Itchy ears, even if asymmetrical, are often a sign of allergic skin disease. Flea allergy will cause severe itching, usually at the base of the tail and along the back legs. Breeds predisposed to atopy include Scottish and West Highland white terriers, Fox terriers, Sharpei, Labradors and golden Retrievers. German Shepherds are prone to food allergies.

Diet can be beneficial in two major ways: provision of omega-3 fatty acids and provision of a hypo allergenic. The first approach to an itchy dog with a dry flaky coat as far as nutrition is concerned is to check the quality of the diet. The cheaper dog foods have a poorer quality protein source and much less oils and fats. Oils and fats in the diet can cause the food to become rancid and thus extra anti-oxidants have to be added and this is costly.

Step one with a dry, poor coat is to improve diet quality. Adding sunflower oil will help to make the coat shiny but will do nothing to stop itching as it only works on the hair. The skin-sensitive veterinary diets have added omega-3 fatty acids. These long chain fatty acids build themselves into the cell walls of many cells in the body.

Normal inflammation causes the breakdown of the fats in the cell walls to harmful by-products. When omega-3 fatty acids have been incorporated into the cell these breakdown products are less harmful, cause less inflammation and benefit skin, joint, heart and kidney disease.

Omega-3 fatty acids can also be supplemented, although inclusion in the diet is generally considered better and is also more cost effective.

The most radical dietary management of allergy is the use of hypoallergenic diets. Proteins are the part of the diet that is most likely to cause a reaction. In these diets the protein source is novel - a protein to which the dog has not previously been exposed, including lamb, ostrich, fish and duck. 

Some prescription diets have gone a step further and have hydrolysed their protein source: chopped up into portions too small for the body to recognise and respond to. Novel protein diets need to be prescribed by a veterinarian as part of a management program. A diet trial is about six to eight weeks, during which nothing else must be fed and response is measured.