Its the sweat stripping the natural oils away that is the problem.
Vaseline as a preventative on areas that might chafe when sweaty. You only need a dab or two and it will do you for all day riding.
Also travel wet wipes to ensure that you are clean after a no 2 is pretty essential.
Sudocream in the event of trouble (or the after effects of unusual food!!)
The little vaseline metal tin, plus a tiny sample pot of sudocrem should do for even week long multiday trips and be weight weenie bike pack friendly.