Flea allergy affected dogs are usually chewing or scratching at their tail-base or around the neck, but they can be itchy anywhere. Unfortunately, it takes only one flea to cause a major irritation for a dog allergic to fleas, which is why some dogs that have very few fleas can be itchier than a non-allergic dog with many fleas. While often a seasonal problem (spring/summer), flea allergy can occur year-round, particularly for inside pets. This is by far the most common type of skin allergy seen in dogs.

Inhaled allergy (or atopy) is relatively common and generally affects all areas of your dog, including the paws, ears, and face. The most common allergens (a substance causing an allergy) are grass pollens, other plant pollens, dust mites and moulds (the latter two being found normally in indoor environments). While often seasonal initially, this allergy can progress to be a year-round problem.

Contact allergy is quite uncommon and usually affects areas with little or no hair covering, for instance, the feet and abdomen. Allergens include grasses, plants, clothing/carpet fibres, hessian bedding and many others. This is often a seasonal allergy but can be year-round, depending on the cause. The most common cause is contact with Wandering Jew; an evergreen, small-leafed creeping plant.

Food allergies often causes dogs to be itchy around the face, ears and feet – although they can be itchy all over. The most common allergens are wheat (found in most canned and dry foods), beef and to a lesser degree, chicken. Food allergies will occur any time of the year that your pet is receiving the allergy-inducing food.

An allergy to bacteria that's normally found on the skin is also called a ‘Staph Allergy’, as Staphylococcus is the most common skin bacteria. This allergy will often cause slightly different signs to the other allergies, but we will be able to determine if this is a factor in your dog’s itchiness. This allergy can also be present year-round and is one which requires specific treatment from your vet.

While it is helpful to group skin allergies into these five groups, due to the similarity in signs, it is impossible to tell on appearances alone which allergen is causing the problem. The allergens mentioned above are the most common sources of irritation, but there are literally hundreds of substances which have been reported to cause allergies in dogs. As well, many allergic dogs are allergic to more than one allergen.

If all of the these options have been performed to no avail, then a contact allergy or inhaled allergy not included in the allergy test, is most likely. Further trials can be performed at home, such as changing bedding or sending your dog to a friend’s house for 3–4 weeks. If a cause can still not be identified, a second option is appropriate.

Antihistamines have drowsiness as their main side effect, which can be remedied by reducing the dose. The effectiveness of each antihistamine varies, even for each dog. For this reason, we suggest trying at least three different antihistamines before deciding if this treatment will work for your pet. All can be purchased from the chemist without a prescription (refer to the adjacent table). Furthermore, antihistamines are up to 50% more effective when combined with a fatty acid supplement.

Fatty acid supplements including Evening Primrose oil are widely available with little risk of side effects. Give 1–4 capsules in food a day, the higher dose for larger breeds. The capsules can also be broken, and the oil applied to food. An alternative supplement (Megaderm) is available from us and may prove more cost effective.

Anti-allergy shampoos and conditioners available from us can be effective in providing at least short-term relief from itchiness (e.g. Epi-soothe and Aloveen). Other products have been reported to help (e.g. Tea Tree shampoos and eucalyptus rinses), but we have had rare allergic reactions reported with these products.