The concept of food avoidance during pregnancy to prevent allergies in children has been the focus of many studies, but with confusing results. With milk, egg and peanut allergies making up 80% of food allergic reactions in infancy, research has emphasized these foods. Other foods such as soy, wheat, fish, nuts and shellfish bring the figure up to 90%. Initial studies focused on mothers' diets during the third-trimester and while lactating, followed by avoidance of specific foods in the infant, such as milk until one year, egg until two years and peanuts until three years old. In the general public, however, the idea that even families without atopic histories would benefit from such approaches has been added "just in case" -- especially with peanuts. Sensitization to antigens definitely occurs during pregnancy, but since it takes place at 22 weeks' gestation, a mother would have to avoid specific foods for a considerable duration of the pregnancy. If several foods were avoided, the fetus might suffer nutritionally. Food avoidance diets don't turn out to affect the onset of asthma or rhinitis, though they may "modify" the course of atopic dermatitis and food allergies. For example, milk sensitivities have a 50% chance of disappearing on their own by the age of one year, 70% by two years and 85% by three years. As it turns out, avoidance isn't preventing, but merely bypassing, the problem. Parents need to be aware that there's still is a chance -- although certainly less -- of a food allergy cropping up with late introduction. With peanuts, studies show that a child has a 1-2% chance of having peanut allergy if the parent is allergic and a 6-10% chance if a sibling has it. Some argue that since peanut is such a strong allergen and isn't nutritionally required during pregnancy, there should be no objection to avoiding it. While this may be a practical suggestion, remind parents that there's no 100% guarantee that the child won't have an allergy later on. Studies are underway to look at vaccines and other genetic modification techniques to prevent or treat these problems. This research may hopefully allow us to use the word "prevention" with a little more conviction. MG