May one place a band-aid on a wound on Shabbos?
Doing so may involve the tearing prohibition when opening it and the sewing prohibition when applying it.
Opening the band-aid: Some Poskim rule that the band-aid must have its wrapping as well as its white plastic sheet which covers over the tape, removed from before Shabbos. Removing it on Shabbos involves the tearing prohibition. However other Poskim hold that the band-aid may even be opened on Shabbos, and doing so involves no suspicion at all of a prohibition. [Seemingly according to Admur it must be removed from before Shabbos.]