Many schools have declared that they are “nut-free,” meaning that the onetime staple of kids’ lunchboxes — a peanut butter and jelly sandwich — is nowhere to be found on school grounds these days. That’s because peanuts can cause a life-threatening reaction in some people. Peanuts are one of the food allergens most commonly associated with anaphylaxis, a sudden and potentially deadly condition that requires immediate attention and treatment.In recent years, awareness about peanut allergy in children has risen, as has the number of peanut allergy cases reported. In May 2010, a study noted that the rate of peanut allergies in children, as reported in a telephone survey, had more than tripled between 1997 and 2008.There are several misconceptions about peanut allergies. A peanut is a legume (belonging to the same family as soybeans, peas and lentils), not a tree nut. And while it was previously believed that an allergy to peanuts was lifelong, research by the National Institutes of Health shows that about 20 percent of individuals with a peanut allergy eventually outgrow it.