Food allergies have to do with a mistake your immune system makes regarding certain proteins. When you eat something with one of the proteins that your body has deemed dangerous, it releases antibodies called immunoglobulin E; the IgE then triggers mast cells, which call upon a team of chemicals. The chemicals -- particularly histamine -- are what cause allergic symptoms. Some children outgrow their allergies by the time they're three or four; some children take longer to outgrow them; other children never outgrow food allergies. The allergies that kids most commonly get over are allergies to eggs and dairy. The allergies most likely to stick around are those to peanuts and shellfish.
Researchers don't fully understand why some kids grow out of their allergies at a young age and some never grow out of them. Even more than that, researchers have noticed that it now takes kids longer on average to outgrow their allergies than it once did. On the whole, somewhere around six to eight percent of kids under five years old have food allergies of some sort, whereas somewhere between three and four percent of adults have food allergies. Until a child outgrows his food allergy, the best method of coping is to avoid the allergen altogether. Unlike food intolerance, even the smallest amount of an allergenic food will cause a reaction. When it comes to food intolerance (like lactose intolerance, for example), symptoms are typically dose-related.
While food allergies are merely uncomfortable for some kids due to rashes, runny noses and diarrhea, for some kids food allergies can be life-threatening. Anaphylaxis is a rare but potentially fatal symptom of food allergies; it's most commonly associated with the allergies that kids don't outgrow, like shellfish and peanut allergies.