Never more than 2 days I guess. There's like no reason for you to skip shower.
no clean running water? poverty?
there's no reason for you to shower every single day, i mean if you start to smell after 24 hours then seek medical help
4 Days, although I did swim in the ocean every day which I guess is a shower in a way. I felt vile though, but I wasn't about to use the ratchet shower next to a Bathroom STALL.