Allergies are another frequent cause of scratching. Most dogs with fleas will scratch to some extent, but a dog with a flea allergy is miserable after only one flea bite. Seasonal pollens, molds, insects, house dust and house dust mites are other common causes of allergies. Food allergies, caused by one or more ingredients in the dog's diet, are the third most common reason for scratching.

For many years, lamb and rice was recommended for food allergy testing, and the public got the impression that it was good for the skin. Now, you can find a fairly wide selection of lamb and rice foods, most of which also contain corn, beef, chicken, and other components. Lamb and rice mixes do provide a complete diet; however, a lamb and rice diet is not inherently better than a normal diet. If veterinarians suspect food allergies, they must turn to more exotic sources of protein such as fish, rabbit, or venison, and carbohydrates such as potatoes or yams.

Another myth regarding dog food is that your dog must stick to the same food for life. Many veterinarians suspect that this creates food allergies over time, and now recommend switching protein types several times a year.