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DOUBLE TAP TO ZOOM WITH PHONE OR TABLET stronger and more resistant to antibiotics, and more of our children are devel- oping diseases, such as allergies and asthma. What is happening? Teachers who have worked with young children for over the past two decades or more are witnesses to the skyrocketing levels of allergies in devel- oped countries. Once peanut butter ruled supreme in the classroom. Children happily rolled peanut butter balls for snack and munched on peanut butter sandwiches for lunch. The gooey substance is now banned for fear that allergic children will develop anaphylactic shock at the mere touch of peanut butter residue. Most teachers in the United States now deal with allergies regularly. The Asthma and Allergy Foundation of America (2014) states that one in five Americans suffers from asthma and allergies. One theory for the escalation of allergies is the hygiene hypothesis, which states that “excessive cleanliness interrupts the normal development of the immune system, and this change leads to an increase in allergies. In short, our ‘developed’ lifestyles have elimi- nated the natural variation in the types and quantity of germs our immune sys- tems need for it to develop into a less allergic, better regulated state of being” (UCLA Food and Drug Allergy Care Center 2014). The hygiene hypothesis has been reinforced by recent studies that show that children who have dogs as pets during their early life (Bergroth et al. 2012) or who are raised on farms (Lewis et al. 2012) have stronger immune systems. As explained by Mary Ruebush in Why Dirt Is Good, From infancy onward, every germ you fight off increases your ability to fight that germ off again later on even more effectively. Every germ you fight off also strengthens the communications among your immune system cells and lets you mount an offense against an invader that much more quickly. When your immune system doesn’t encounter a lot of dirt, it doesn’t get challenged. Instead 8  •  Chapter 1 COPYRIGHTED MATERIAL