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Living on the planet Mars would pose a number of significant challenges and changes to the human body.
Mars has a gravity approximately 38% of Earth's gravity, which means that colonists would experience a decrease in muscle strength and bone density due to the lack of gravitational resistance.
The Martian atmosphere is extremely thin and composed mainly of carbon dioxide, which means that colonisers would have to deal with a lack of oxygen and the need to wear spacesuits to protect against solar radiation and extreme cold.
In addition, Mars has a much lower atmospheric pressure than Earth, which would cause body fluids, such as blood, to boil at normal temperatures.
This means that colonisers would have to live in pressurised environments to avoid serious injury.
Which is why, unless profound changes occur in humans when they reproduce there, the red planet is not at all friendly to human life.