Near the end of The Martian movie we see Mark Watney shirtless, and his body appears to be bruised. What is the cause of these marks? I thought it might be from scurvy or some other malnutrition.
When Mark takes the suit off in the ship at the very end of the movie everybody complains about his body odour.
He says " I haven't had a shower in a year".
Having been in a similar situation ( with no acces to water for a long period of time ) I can tell you that his marks look a lot like something you get from not enough personal hygiene combined with a poor diet.
I was struck by the skin lesions/rash as well, and have been looking for an explanation. I suspect it had to do with prolonged exposure to radiation. The Mars atmosphere is very thin, 100 times less dense than Earth's. An astronaut wouldn't have the same protection from solar radiation that we enjoy on Earth.