Just one bite of cake that is made with eggs is enough to make John feel very sick. Susan gets a terrible rash whenever she eats anything containing seafood, and David nearly died when he first ate a cookie that included peanuts. David had trouble breathing after he ate the cookie, but his mother knew what to do and she quickly gave him medicine that helped him feel better almost right away. The body's reaction to certain foods can be quite severe, resulting in breathing problems, as in David's case, or loss of consciousness for some. There are many things we eat may cause our bodies to react badly if we have a food allergy . The most common food allergies seem to be related to milk, soy, eggs, wheat flour, peanuts, nuts, and seafood. In fact, these kinds of foods account for 90% of food allergies. According to some studies, the number of children who have a food allergy is growing. But some people now argue that test results might not actually be accurate, so food allergies are not really as common as they may appear. There are three typical ways that doctors test for food allergies. Probably the most accurate way is for a doctor to give a child a  food challenge", For this, the doctor watches the child eat small amounts of certain foods to see if the child has an allergic reaction or not. This method is very time consuming so it is used less often than the other two methods: skin tests and blood tests. In a skin test, a doctor puts very small amounts of the parts of the foods that the child may be allergic to under the child's skin, then watches to see if the child's skin reacts to the allergens . In a blood test, doctors take some of the child's blood and add possible allergens to it and then look for chemicals in the blood that indicate a possible allergic reaction. A problem with both the skin test and the blood test is that neither will show how severe an allergic reaction might be. If a test result is positive, the child may have a severe reaction by eating this food, but the child might just as likely only have a slight rash. The test will not show which of these might be the case. Dr. Jennifer Chafen of Stanford University studied 10 years' worth of allergy research to check how accurate the tests are. She found a surprising fact. Skin tests or blood tests given to patients who visited their doctors for treatment of rashes or stomachaches showed that these patients were allergic to certain foods. However, later tests showed that although these patients tested positive, fewer than 50 percent of them actually had blood allergies. So were the results false and can we rely on these test results?  The problem might be food intolerance rather than a food allergy. While foodallergies are mainly related to a person's immune system, food intolerance is related to a person's digestive system and the reaction is usually less severe. One of the most common kinds of food intolerance is related to people who have trouble digesting the sugar in products like milk, cheese, and ice cream. Doctors are not sure why the number of cases of food allergies is rising. One factor that may explain part of the problem is our cleaner environment. Most children are exposed to fewer germs these days and some researchers think that for some people, their body's immune system makes work for itself by reacting as if certain foods are harmful. While allergy test results may show false positive results, the tests are still useful and can save lives. Some children lose their food allergies as they get older, so even though doctors do not have a cure for food allergies, sometimes the body finds its own cure. What is the passage mainly about?
Different kinds of allergy tests. A new allergy test that works very well. When children should be tested for allergies. How allergy tests have changed over time.