The "hygiene hypothesis," backed by some but not all studies, suggests people are more prone to allergies and asthma when they're not exposed to germs early in life. Why? Their immune systems haven't learned what's dangerous, such as bacteria, so they overreact to allergens, which are otherwise harmless.
A new CDC report suggests pediatric rates of hay fever, more common than drug or food allergies, remained stable from 1997 to 2011, based on interviews with parents. Co-author Lara Akinbami, a CDC pediatrician, says hay fever may still be increasing but, since its symptoms are similar to those of the common cold, parents may not recognize it as a seasonal allergy. They also might simply be treating it with over-the-counter medicines.
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Though some plants grow more food or flowers as a result, more pollen can spell trouble. Doctors say it's contributing to a rise in seasonal hay fever and allergic asthma in the USA, where the pollen season has lengthened up to 16 days since 1995. If carbon dioxide emissions continue to increase, they expect allergic conditions probably will worsen, adding to the discomfort of allergy suffers as well as swelling U.S. health care costs.