The human microbiome (or human microbiota) is the collection of microorganisms which live on us. They live on the skin, in the saliva and mouth, in the eyes, and in the gut and the rest of the gastrointestinal tract. They include bacteria, archaea, fungi and single-celled eukaryotes ('protozoa'). Everyone carries around far more of these microbes than the number of human cells in the body. The human body has about 100 trillion cells, and carries about ten times as many microorganisms "in the intestines alone".