Allergy as defined is the state of hypersensitivity of the body to certain substances known as allergens. These   are substances to which one is exposed in any form. They may be present in the atmosphere, which one may inhale. It may be available for local application on the body or may be ingested in the form of food or drinks.  Among all these allergies, allergy to food substances is the most troublesome. Somebody having allergy to a food substance may not be aware of it. He or she may be consuming that item everyday and getting sick. He may not be aware of the fact that a particular food item or one of its ingredients is making him sick.  The body becomes sensitive to a particular substance in the food and reacts by producing antibodies. Thus on subsequent exposure to the food substance, an antigen, antibody reaction is triggered, manifesting in various ways.Food allergy manifests in the form of skin rashes, itching, dry cough, sneezing or running of nose, breathlessness, swelling over eyes and throat. A person may have one of these or many of these complaints together after exposure to the particular allergen (allergy producing substance).  Diarrhea, nausea and vomiting may also occur in some persons due to food allergy. Food allergy is    different from the sickness caused due to food poisoning which is caused due to infectious germs present in contaminated food or drinks.These symptoms may be present chronically if someone is consuming the allergy producing substance daily or it may occur acutely if it is a one time exposure. At times the allergic manifestation may be severe and fatal.One may have allergy to the natural ingredients in a consumable item, like proteins present in eggs, soy products, milk and milk products   or   nuts. There may be allergy to the spices used in cooking a particular dish.  One may have   allergy to chemicals present in foods. This is in fact one of the most common   cause of food allergies occurring in the developed western countries.  These chemicals are used for preserving the food or enhancing the flavor or color or as emulsifiers.   This sort of allergy develops mostly with preserved foods or instant ready to eat foods.One needs to be aware of food allergies to be able to identify problems occurring after consumption of some type of food. Otherwise he or she may spend their time and money in visiting doctors and undergoing various tests to find the cause for the underlying illness. The picture gets more confusing if somebody has diarrhea or vomiting as one mostly suspects food poisoning in such cases. A   high degree of suspicion is needed with tests to establish diagnosis of food allergy. Diagnosis becomes easy if there is a history of allergy in the family among blood relatives in form of rashes or recurrent cold or bronchial asthma. High level of eosinophils, (a type of white blood cell   indicating allergy)   in the blood are suggestive of allergy. Another type of test used for diagnosing food is the intradermal skin test. Potential allergens (allergy producing substances) are injected subcutaneously) and the reaction produced (in form of a flare or wheal over the skin) is read after 48 hours. But this test can be done only when one has no problem for minimum 2 days; otherwise there is a risk of producing a severe fatal allergic reaction. Food planning and   challenge is useful for diagnosing food allergy and also in identifying the food items which produce the allergy. One should try to omit one food item from the   diet    for   2 to 3 days and then re include it. In this way it will be possible to pin point the allergy producing substance. Any food substance   producing   allergy, when consumed, will produce illness in that person. On avoiding that substance, the   person will remain healthy.  Processed or ready to eat fast foods should be avoided. Infants having allergy to milk are given whey or formula feeds.There is no root cure for this problem. Hence one has to be aware of it. Dr. Rachna Pande is a specialist internal medicine