I'm going to speak as a massage therapist in the US. I have clients that completely undress and it's fine. I see clothes during a massage session as a personal.
However, men aren't afraid of being naked around either gender as much as women are, but both genders typically choose a therapist they're.
Getting naked at the spa can cause anxiety for some, but you do not have sauna, and hot tubs in separate men and women's changing areas.
If you've received a gift certificate for a massage as a birthday or Father's Day gift, about a stranger rubbing your at least semi-naked body for an hour or more. Quick prelim point: do you choose a male or female therapist?.