Allergies are abnormal responses to typically nontoxic substances; so why do some kids’ immune systems misread and overreact when others’ don’t? While a family predisposition is often a factor, recent studies also suggest this oversensitivity might be linked to antibiotic overuse—which might help explain why allergies have been on the rise for the last 40 years. “Antibiotics kill off not only disease-causing bacteria but also health-promoting bacteria,” says Gary B. Huffnagle, PhD, of the University of Michigan. “We’re learning that the immune system receives important signals from these beneficial bacteria that train the immune system to attack invaders quickly and then slow down before causing any damage to the body itself. In the absence of ‘slow-down’ signals, the immune system could itself be the cause of chronic inflammatory diseases like allergies.”

Some scientists are taking a hard look at vaccines, too. In his new book, The Holistic Baby Guide (New Harbinger, 2010), Randall Neustaedter, OMD, cites research that links allergies to vaccines. “Some researchers think that vaccination of children tends to create an imbalance in the immune responses, making children more prone to allergic responses.”