Explore the unseen organisms that live on our bodies.

This lists the logos of programs or partners of NG Education which have provided or contributed the content on this page. Program Mysteries of the Unseen World (logo height 65 pix)

  • Microbes are organisms that cannot be seen with the naked eye. They include bacteria, archaebacteria, protists, viruses, prions, and some fungi. They account for most of the diversity of life on Earth. Far more microbes inhabit a single person’s body than there are people on the planet. Microbes also dominate in terms of their ability to live and thrive in extreme environments, including clouds, deep sea volcanoes, hotwater springs, polar ice caps, and human intestines.


    Most animals, including humans, exhibit numerous associations with microbes. Microbes live in and on their skin, hair, mouths, and guts. In fact, many animals contain fewer of their own cells than microbe cells. Microbes play an important role in the health and survival of most animals.


    Humans typically associate microbes with disease. However, most microbes are more beneficial than harmful to humans. Often, their effects are neutral for their human hosts. Microbes help to digest food, absorb nutrients, and out-compete harmful bacteria in the intestines. They produce vitamins and proteins that human genes cannot produce. They prevent the growth of harmful skin bacteria and further aid the immune system in fighting infections and diseases throughout the human body. 

    • The microbes that inhabit a single person outnumber the human cells ten to one and can weigh approximately three pounds.
    • Streptococcus bacteria are responsible for most tooth cavities and are a leading cause of oral infections.
    • E. coli is one of the most well-studied bacteria because it can cause severe intestinal illnesses. When kept in check, however, it plays an important role in providing humans with K and B vitamins.
    • Lice are parasitic, blood-feeding insects found on human heads and bodies. They are spread through close human-to-human contact.


National Science Foundation Mysteries of the Unseen World

This material is based in part upon work supported by the National Science Foundation under Grant No. DRL-0840250. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation.

Made Possible in Part By