While food allergies are not as common as atopy, they can affect your dog at any age. Oddily enough, most allergic reactions are to foods that a dog has been eating for a long time. If your dog has an immediate adverse reaction to a new food, it’s probably not an allergy, because it takes more than one exposure to produce an allergic reaction. The signs are very similar to those of other types of allergies, so it's not always easy to tell the difference. Signs to look out for include: itchy skin, especially around the face, paws and ears, ear infections, self-inflicted skin wounds, unpleasant skin odour, excessive scaling, red bumps or pimples, diarrhoea and vomiting (quite rare). Before you have expensive tests done, try a home elimination test: look for reactions after your dog has eaten food more than once, feed your dog a diet they haven’t been previously exposed to twice. If you’re still stumped, consult your vet.