I mean, think about it. Walking around in the same black leather outfit all the time - does he ever even bathe? Does he ever take it off? Can he even? Parts of it are parts of him! We know he takes the helmet off sometimes, but even there the closeness of the helmet and the rankness of dried spittle must be overpowering. The suit probably has some climate-regulating elements, but go ask an astronaut how rank their kit gets after a full day's work - and they're not striding around menacing people 24/7 in it. There's no in-film evidence that the Empire's technology has developed any B.O.-killing miracle fabrics. Look at Grand Moff Tarkin! His foul stench carries all throughout the Death Star, and his outfit is clearly far more breathable than Vader's.
It's kind of disgusting when you think about it.