Cats can suffer from the effects of food allergies in a similar way to humans, and this is often seen in the form of a skin disease and dermatitis. Food allergies are caused by an unusual biological reaction to a foodstuff that would normally be considered harmless, when the immune system first rejects it and then mounts an immune response against it. It is very important to keep the immune system fully functioning in any creature, as it serves the purpose of keeping the body free from certain 'bad' bacteria, infection, viruses and fungi. The most common causes of food allergies in cats are fish, beef, eggs, wheat and milk, the latter being extremely common. In times gone by it was usual to give cats a saucer of milk to drink, but many cats nowadays (both pedigree and non-pedigree), are allergic to cows' milk, which often causes stomach upsets and diarrhoea at the very least. Cats can even become allergic to food that they have previously eaten over a long period, in the same way that humans develop food allergies to things they have always eaten, and for no apparent reason. It's also worth thinking about whether your cat could have eaten something else that might have disagreed with him, such as some of your food, or that of another pet you have. Symptoms of feline food allergies include non-specific itching (where other causes such as fleas, poisonous plants etc have been ruled out), particularly on the front half of the body, including the head and neck and quite often ulcers, crusting and weeping sores on the belly and legs. The ears often become swollen and infected, with significant hair loss due to excessive scratching and grooming, and there is often vomiting and diarrhoea.First of all, your Vet will first want to eliminate all other possibilities such as gastric upsets, internal and external parasites (including worms, fleas, lice and mites), as well as infections, and diseases of the kidney, liver and pancreas. He will also suggest very rigorous flea treatment on the affected cat and all of his housemates, and carpets and furnishings will also need to be thoroughly treated to make sure that this is not the problem. It's difficult to work out exactly what is causing a reaction yourself without subjecting your cat to further distress whilst you try and eliminate the root of the problem by trial and error, and the best thing therefore is to let your Vet carry out controlled food trial tests lasting a couple of months, that should be able to pinpoint the exact cause. In this instance your cat will be put on a special diet, either 'prescription' or home made, that will include food that they have never eaten before such as rabbit, duck or even venison, and probably a carbohydrate. During the trial period you will be asked not to give any other food or treats, and no vitamins or supplements that will invalidate the results. After the trial, if the allergic reaction has disappeared, you will be asked to gradually put your cat back on its original regular diet, and if the symptoms then return, you will be able to work on tracking down exactly which ingredient is causing the problem by a process of controlled elimination, gradually introducing the previous contents one by one. As with humans, it will be relatively easy to manage the situation once the rogue foodstuff has been identified. It will be very important to ensure that your cat does not have access to this particular food in future, which will mean feeding all other cats on exactly the same diet so that the allergic cat does not help itself to something that will cause an adverse reaction. You will also need to make sure that you tell the owner of the cattery if you are boarding your cat whilst you are on holiday, and give them a very specific diet sheet to follow. Make sure also that any family and friends who might feed your cats are aware of the dietary needs of your allergic cat and it would be a good idea to post a list of prohibited items near where you feed your cats, just in case. Both during the trial period and in managing the situation, it will be best for the health of your affected cat if you can keep him indoors, and help him adapt to an inside lifestyle so that he doesn't steal any food that causing the allergic reaction from neighbours' houses or out in the garden. However, in the event that the symptoms do not clear up after food trials, it is often a good idea to ask your Vet to refer you to a specialist. Certain inflammatory and other bowel conditions can trigger a food allergy, which can only be diagnosed effectively by endoscopic investigations and biopsies, and a vet who specialises in gastro-enterology will have the necessary equipment and expertise to carry out these tests.Closely linked to food allergies is intolerance to certain foods, which is different to an allergy in that the immune system is unaffected. It could be compared to humans who are intolerant of dairy food or highly spiced food, and who will suffer from a similar discomfort and reactions. The most common intolerance is linked to milk, and like an allergy, your cat will probably suffer from vomiting and diarrhoea, but in addition there will also be abdominal pain but probably no sign of itching or skin disease. Food intolerance can be tested in the same way as a food allergy but can be slightly more difficult to pinpoint.You should take any cat suffering with symptoms potentially indicating a food allergy (or intolerance) to your Vet as soon as possible. Your pet insurance should cover most of the associated costs (although probably not the alternative diet during the test periods), so long as your cat was insured before the symptoms manifested themselves, as pet insurance policies will not cover an existing condition.