At sea-level, Earth's atmospheric pressure is 14.7 psi and Mt Everest summit's is about 4 psi. Mars' atmospheric pressure is about 0.087 psi. Apparently a pressurized suit is required to survive on Mars[1].

Also, Mars' soil has toxic amounts of perchlorates[2]. You wouldn't want to breathe them in or have them touch your skin.

[1] https://www.quora.com/Is-it-possible-to-breathe-and-survive-...

[2] https://www.space.com/21554-mars-toxic-perchlorate-chemicals...