In fact, muddy dirty play is incredibly good for you. According to research, playing outside in the grime and muck has health benefits for your heart, skin and immune system. Plus, studies show enjoying a good clean (dirty) day in the dirt increases happiness, reduces stress and enhances learning. Really. Here’s some reasons to encourage you to back away from the hand sanitizer, laundry soap and hand towels, and embrace the gloriously goopy joy of nature’s immune-system-builder extraordinaire.