What substances are most likely to cause a severe reaction?

There are many possible allergens, but these are the most common:

• Peanuts, tree nuts (such as walnuts and cashews), shellfish (like shrimp and lobster), fish, milk, and eggs are the most common culprits, although any food can cause a severe allergic reaction. (A great deal of research is being done on whether delaying the introduction of potentially allergenic foods will delay the onset of allergies in allergy-prone children. If food allergies run in your family, your child may be more susceptible.)

• Drugs in the penicillin family (including the popular antibiotic amoxicillin)

• Insect bites and stings (especially from bumblebees, honeybees, yellow jackets, hornets, wasps, fire ants, and harvester ants)

• Latex (often used in healthcare facilities)

• Food preservatives and colorings (like FDC yellow No. 5)