Dr. Stephen White, a professor of dermatology at the University of California, Davis, School of Veterinary Medicine, answers this week's questions about food allergies.
Question: What is the difference between a food allergy and a food intolerance?
Answer: Food allergy denotes an immune response to a food; food intolerance presumes no immune response. In veterinary practice the difference is difficult to distinguish, and probably not clinically important in most cases, and the more general term cutaneous adverse food reaction (CAFR) is often used.
Question: How common are actual food allergies?
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Answer: This is debatable, as many cases are probably noted by owners (particularly if there is vomiting or diarrhea involved with the feeding of a new food) and never reported to veterinarians. A rough estimate would be around 5 percent of dogs, probably the same in cats.
Question: How does a food allergy present itself?
Answer: The most common clinical sign of food allergy affecting the skin in dogs is nonseasonal scratching, which is usually generalized. This also may be primarily directed at the feet or ears.
The most common lesions that the owners see are a red rash, scaling, or an increase in skin pigmentation. In cats, small crusts or facial/head/neck scratching are common. Of course, there are other causes of all of these signs.