In S03E04 episode of Voyager (The swarm) we see the Doctor aka EMH, prepare to operate on Lt Tom Paris. Surprisingly, he seems to be sterilising his hands with a machine that emits a faint red light. Of course that could be for something else, but he explicitly says he's scrubbing
KES: Doctor, I have the cortical analeptics you asked for.
EMH: Good. Fill the hyposprays, we'll begin as soon as I've finished scrubbing.
However we know that the Doctor is a hologram and can at will alter his projection, so he could, for example disable the forcefield momentarily to get rid of the bacteria and then enable it again so as to operate.
Why did he need to scrub in before the operation?