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| - Earth's population is estimated to be roughly 8 million people, according to the United Nations. Depending on body size and thus the surface area of skin, a person could have more than 8 billion individual microbes living on their skin, according to a 2015 peer-reviewed study and the U.S. National Library of Medicine.
However, smaller people with skin that covers smaller surface areas might have fewer than 8 billion individual microbes on their bodies. Also, a "life form" could be defined as a species of microbe or an individual organism. If using the former, scientists estimate a person has about 1,000 on their skin.
Posts claiming that a person carries more "life forms" on their skin than there are people on Earth have long circulated on social media, dating back more than a decade.
(Reddit user u/butrcupps)
The claim's level of factualness depends on a person's size and how "life form" is defined. The Earth's population is estimated to be roughly 8 billion people, per the United Nations. Depending on body size and thus the surface area of skin, a person could have up to 20 billion individual microbes living on their skin, according to a 2015 peer-reviewed study
However, smaller people with skin that covers smaller surface areas might have fewer than 8 billion individual microbes on their body.
Also, a "life form" could be defined as a species of microbe, such as bacteria, or an individual organism such as Staphylococcus aureus, which causes skin infections. If using the former classification, scientists estimate that a person has about 1,000 species of microbes on their skin.
Answer Depends on Body Size, the Definition of 'Life Forms'
A 2015 peer-reviewed
The normal microbial counts using culture methods typically range from 10^3 [1,000] to 10^4 [10,000] organisms per square centimeter with counts reaching a high of 10^6 [1 million] per square centimeter in the most humid areas such as the groin and axilla. (Cundell, 2015)
According to the U.S. National Library of Medicine, depending on body height and weight, a person's skin covers an area of up to 2 square meters:
Even at its thickest point, our skin is only a few millimeters it is still our heaviest and largest organ, making up about one seventh of our body weight: Depending on your height and body mass, it weighs between 3.5 and 10 kilograms (7.5 and 22 pounds) and has a surface area of 1.5 to 2 square meters.
Using these figures, we calculated a person could have as many as
However, the math works differently if "life forms" are interpreted to mean species of microbes.
The U.S. National Institutes of Health said in 2022 that around 1,000 species of microbes live on a person's skin. In other words, under this interpretation, fewer species of microbes live on a person's skin than there are people on the Earth.
Scientists have long studied the amount of microscopic organisms not just living on humans' skin but also living inside their bodies.
For example, research published in 1977 estimated the ratio of bacteria to human cells
The New York Times has reported on 2016 research challenging those older studies. In January 2016, a group of Israeli scientists published research drastically reducing the estimated number of individual
While that amount far exceeds the population of Earth, the figure is an estimate for the whole human body, not just skin.
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