Scratching is a very common symptom in dogs, and you as an owner should aim to nip it in the bud early before self trauma causes secondary injuries to your dog. However, before wondering whether your dog could have an allergy, you must rule out the common parasitic (fleas and mites), bacterial (hot spots) and fungal (ringworm and yeast) infections. See my article Is your Dog Scratching to explore these in greater detail.
Just as allergies have become more common in children these days compared to several generations ago, veterinarians are seeing far more allergies in pets too. It is difficult to explain this phenomenon, theories range from alterations in the content of pet foods to the use of modern day household cleaning products or simply genetic evolution. One thing is certain, whatever the cause, allergic dogs benefit hugely from avoiding the offending allergen or, if that is impossible, appropriate treatment to minimize the itchiness.
Lets start with the presenting signs of an allergy in dogs. Itchiness can manifest itself not only as obvious scratching at the neck and flanks, but also as face rubbing, foot licking or chewing and over grooming. Foot licking, for example, is often perceived by owners as normal, when in fact the dog is responding to itchy feet in the only way it can, by licking them. The skin between the toes may turn red and sore due to the compulsive licking, and in white dogs such as West Highland White Terriers and Bichon Frises, the fur is stained brown by saliva.
Ear infections are another common sign of an underlying allergy. Though general waxiness, hair in the ear canals, lack of ventilation, bacteria and yeast may trigger the infection, an underlying allergy is often the root cause of the itchiness. If your dog gets recurrent ear infections, by eliminating an underlying allergy you may prevent your dog from going over the itchiness threshold and developing full blown ear infections.
So, what are the common allergies in dogs?
For convenience they are best separated into 4 categories.
1)Flea bite hypersensitivity
2)Adverse food reaction
Flea bite hypersensitivity is relatively straight forward to cure. It is a simple case of eliminating every single flea on the dog and, crucially, in his/her environment. The itchiness is caused by an allergic reaction to the flea saliva, and so even a solitary flea can trigger a scratching frenzy. To rule out flea bite hypersensitivity, all animals in the house (dogs and cats) should be treated with a reputable veterinary spot on medication monthly without fail, and the house should be thoroughly sprayed with an insecticidal spray.
Adverse food reactions are more difficult to treat as it can be difficult to isolate the precise ingredient responsible for causing itchiness in your dog. Not only that, treating adverse food reactions requires owners to be exceptionally disciplined and motivated in preventing their pet having even a single treat unless the exact ingredients are known to be safe.
There are two ways of diagnosing an adverse food reaction (also known as a food allergy). For those readers for whom cost is not an issue, a blood test can be done to measure for ingredient specific antibodies in the bloodstream. The blood test is quite costly, and if combined with a blood test for environmental allergens is usually upwards of $400 (£200). The company performing the blood test then provides a list of ingredients (chicken, beef, pork, rice, wheat etc) and a score next to them, suggesting which ingredients are best avoided. The owner then picks a commercial diet which does not include any of these ingredients, or indeed a special home cooked diet. The second way to diagnose an adverse food reaction is to conduct a dietary trial. This involves picking a very bland hypoallergenic diet and feeding your dog exclusively that for at least a month, preferably 6 weeks. The author usually suggests turkey and rice, as less dogs are allergic to turkey than chicken. Of course if your dog happened to be allergic to rice or turkey, which is rare but nevertheless possible, you would be none the wiser as the itchiness would continue and you would assume you had ruled out a food allergy having done the turkey and rice dietary trial. Remember if you are doing one of these trials, then your dog must not be given any treats, especially not pigs ears, chews, boneos, dental sticks or any rawhide products. Literally nothing must be swallowed other than turkey and rice (and water!) for the entire trial period.
If you have ruled out flea bite hypersensitivity and ruled out an adverse food reaction, the next step is to consider an environmental allergy, also known as atopic dermatitis. Symptoms of atopic dermatitis usually begin between 1 and 3 years of age, though any age is possible. The itchiness is often seasonal, which is consistent with a pollen allergy, though some dogs are itchy all year round. There are certain breeds which are predisposed to this condition: Boxers, Bull Terriers, Dalmations, English Bulldogs, German Shepherd Dogs, Golden Retrievers, Labrador Retrievers, Shar Peis, Shih Tzus and West Highland White Terriers being the most commonly affected. Diagnosis is usually made based on the history and ruling out all the other causes of itchiness, and many vets will treat the condition on these presumptions. However, definitive diagnosis can be achieved via a panel of injections into a patch of skin, or blood tests. Neither of these are particularly effective and generally not performed unless the owner is prepared to attempt a desensitization programme. This involves a long term course of injections given by your vet on, say, a monthly basis to desensitize your dog to the offending allergen, and so make the allergic reaction much smaller when he/she does come into contact with it.
Contact dermatitis is a skin reaction caused by your dog coming into contact with a chemical that is an irritant. It therefore only tends to affect the stomach, groin and feet of the dog, and is characterized by reddening and drying of the skin in these areas. It can also be seen when owners shampoo their dogs with a product that is not intended for use in dogs. Contact dermatitis is rare, but easily ruled out by careful use of cleaning products around the household. Just think, did the itchiness coincide with the introduction of a new carpet cleaner, washing powder or fabric softener?
By far the best treatment for any allergy is avoidance of the cause. By careful investigation and following the steps above this is often possible, especially for flea bite hypersensitivity, adverse food reactions and contact dermatitis. If avoidance is impossible though, as is the case for many cases of atopic dermatitis, then seasonal or lifelong treatment may be indicated. Steroids are very effective at stopping itchiness caused by allergies, but long term use can lead to undesirable side effects, such as adrenal gland disease. Long term steroid use should only be used as a last resort, when other medications have been tried and failed. These other medications include antihistamines, essential fatty acids and medicated shampoos.