Fixed (immediate) food allergies: A fixed food allergy may be very apparent, such as the child whose lips swell and throat itches immediately in response to eating peanuts. The cause for this type of food allergy is similar to that of inhalant allergies, so the diagnosis is more easily reached. Blood testing (i.e., RAST test) is typically used to verify fixed food allergies. Approximately 5 to 15 percent of food allergies are of the fixed variety.
Cyclic (delayed) food allergies: These allergies are far more common but less understood. Delayed food allergy symptoms can take up to three days to appear. This type of reaction is associated with the body's immunogobulin G (IgG) or antibodies. Unlike fixed food allergies, this allergic response is cyclical in nature. As an example, a child may be IgG sensitive to milk. Consequently, symptoms might appear if the child increases the intake and/or frequency of milk consumption.
Both children and adults are susceptible to food allergies. The bad news for children is that they often have more skin reactions, such as eczema, to foods than do adults. But the good news for the young patient is that a child often outgrows his or her food sensitivities over time, even those that are positive on a RAST test. Food allergies may fade, and then inhalant (e.g, dust, ragweed) allergies may begin to manifest themselves.
If your child is experiencing allergic reactions to food of unknown origin, you should ask, "Are there any foods that my child craves or any food that I avoid offering?" These foods may be the ones that are causing difficulties for the young patient.
Conduct an elimination and challenge diet at home based upon your physician's assessment of your child's diet diary. It is best if you carefully maintain a new diet diary for your child during this period. During this diet, your child must abstain from one, and only one, of the possible food culprits at a time for a period of four days. This can be difficult to carry out if the food is very common, such eggs or cereal, so you need to pay strict attention to your child's diet during the elimination phase. Any cheating will invalidate the results. On the fifth day, you will be asked to feed your child the suspected culprit food item. This is the challenge! Provide your child an average-sized portion of the food in question to be eaten in five minutes. In one hour the child should eat another half portion if no symptoms have developed. Any symptoms that develop are then timed and recorded. With a true cyclic food allergy, you would expect a significant worsening of the symptoms described in the original diet diary, although the challenge symptoms may vary as well.
For minor, moderate discomfort from the testing, the caregiver may choose to offer one the following: 1) a child's laxative to decrease the transit time through the digestive system; 2) Alka Seltzer Gold; 3) Buffered Vitamin C (one gram).