Q: My terrier has been itching a great deal this summer and autumn. My vet diagnosed a food allergy, but after trying several diets there has been no improvement.--H.D. A: Food allergy is thought to be associated with hypersensitivity to antigenic materials (which cause the body to produce antibodies) in the food. Clinical signs can be quite similar to other skin disorders--including flea-related disorders, recurrent moist dermatitis and seborrhea--which can make a definitive diagnosis difficult. If signs abate after a dietary trial of up to 21 days, using lamb and rice as the sole intake, a diagnosis of food allergy can be made. If there is only a minimal response by 21 days, some other disorder is likely. If your pet's skin disorder is seasonal, food allergy is unlikely.