It’s still a counter-intuitive idea to many, but exposure to dirt leads to a healthier immune system. The naturally occuring microbes in our outdoor environment help program the body to learn what types of foreign agents are actually harmless. This prevents it from later attacking innocuous allergens, or even your own body. So one of the best ways to protect your children from a lifetime of allergies and autoimmune disorders is to make sure that they—and you—spend plenty of time outdoors getting dirty.