Microorganisms are distributed everywhere in nature and on both human and animal bodies. Microorganisms include beneficial microorganisms and harmful microorganisms. Of these, only a few species of microorganisms cause disease in humans.

The skin is the largest organ in the body and is also the place that is most often exposed to the external environment. There are millions of bacteria that live on the skin, including beneficial and harmful bacteria, creating a balance for the skin's biological barrier.

Recent studies in humans and mice show that exposure to environmental microorganisms helps prevent allergies and other inflammatory diseases.