How many species live on or in the human body?
It is estimated that around 500 to 1000 different species of bacteria live in or on the human body, including 80 in the mouth alone.
This includes lice, tapeworms and bacteria. The total number of bacteria excreted by the body every day ranges from 100 billion to 100 trillion.
Every square centimeter of human body is home to around 10 billion microbes.
Some 10 million organisms occupy every square centimeter of flesh.
The most densely populated areas of the human body are the teeth, throat and alimentary tract, where the concentrations are increased by a thousand compared to bare skin.
But while such figures seem huge, it has been calculated that the amount of bacteria on the skin of the average human would be the same size as a pea.
That is to say nothing of the common parasites found on the human body. The follicle mite, found on every individual, spends its days harmlessly munching dead skin cells.
Which is less than can be said for Naegleria fowleri, an amoeba that invades the brain and multiplies until the host drops dead.