Normally, when cutting into a hairy part of the body, I assume the area is shaved first if things are planned ahead. Obviously having hair over the spot where you want to operate would make things difficult and could introduce dirt/oil/whatever into the opening.
So what happens when I get a nasty head wound that needs to be closed? (I’m thinking of something like scalping) How do you deal with the hair near the wound? And does dirty hair cause a risk of infection?
It usually get shaved off. Hopefully not too overly-enthusiastically.
Yep. Maybe some numbing agent around the area first, then clippy clippy!
Yes, you will look silly afterwards.
Yup, my husband fell when he was a teenager and got a decent-sized cut on his scalp. He went to the ER because it was bleeding in a big way; they shaved a patch around the area, then stitched him up.
I’m picturing them numbing the area, pulling it taut-ish, then shaving as best as possible. Does that sound accurate?
Pretty much. They have to get down to the skin to be able to repair the damage, so hair is contra-indicated. Although sometimes the “numbing” is skipped. 
Shaving hair does not change the infection rate, although clipping it shorter can make it a bit easier to do elective procedures.
I occasionally shave a wound if it’s really jagged and deep and I need good exposure to see what’s going on or clean up the edges but I don’t typically bother to shave ordinary scalp wounds. They don’t get infected whether or not you shave them, it looks stupid and it’s not necessary. In a pinch you can actually use hair to tie across the wound although it’s a pretty half-assed way to close a wound.
Incidentally most ordinary scalp wounds can be stapled, at least for the skin component.
One disadvantage of not shaving is that it makes it harder to make sure all the closures are removed. Staples are pretty easy to find and if we suture a wound sometimes we’ll choose a blue suture material and also leave the ends long enough to find more easily…
Using the hair to tie across… I’m not sure if that belongs in the “Good to Know” file, but it does sound cool in a gross way.
I had a cyst removed from my head and they didn’t shave it at all. Of which, I was most appreciative.