Q: Dear Dr. Theriot: My 11 month old son appears to be developing food allergies. Although he has been happily eating eggs, drinking whole milk and munching bananas for a couple of months now (with our pediatrician's okay), a few days ago he began to break out in hives whenever he consumes these foods. Is this something that will just disappear as mysteriously as it appeared? Will things just get worse as he continues to eat these foods?
A: If I understand your question correctly, the hives started "a couple of days ago". If this is the case, then your question is going to be difficult to answer definitively. The reason for this is as follows: Hives is an allergic reaction of the skin that causes welts, or "urticaria". The hives are typically transient, meaning that they come and go without any rhyme or reason. Within a few minutes, you may observe a red, blotchy area on the skin that develops into a raised "welt" that becomes intensely itchy...to find that it has completely gone away within minutes...to be replaced by a welt somewhere else on the body.
The causes of hives can be foods, medications, insect bites or stings, one of a number of different viruses or even strep infections. Unfortunately, in most cases of hives, the culprit is rarely identified.
Once hives start, the rash can come and go for a number of days, and there is no stopping the reaction. Steroids can modify the reaction, however, these are rarely necessary. This is what makes your question so difficult to answer. Because your son's hives have been there for "days", doesn't mean that it is necessarily related to any of the foods that you mentioned. It could very well be caused by something entirely different.
As for food allergies, over 90% of all food allergies in children are caused by milk, wheat, soy, peanut, corn and egg. This is not surprising because these foods comprise the bulk of what infants and toddlers eat.
To put this issue to rest, my advice to you is this. Eliminate all the "suspected" foods from your son's diet. Wait until you are sure that the hives have gone away completely. Then I would introduce one of the suspected foods at a time. Be sure that there are no other "new" foods that you are giving him, and let him have that food for a full week. If the hives do not recur, then that food should not be considered a problem. You can then move on to the next suspected food and give it a one week trial...and so on.
If your son is truly allergic to one of those foods, the hives (by definition) will recur upon the re-introduction of the food. The only way for you to sort this out with certainty, is to approach it in a systematic manner whereby you have full control of all the variables.