I know a whole bunch of people on another site that have said their BG drops with hot showers, one even purposely takes hot showers when she needs her BG level to drop.
Mine on the other hand increases drastically, 60 points in 20-30 minutes of a hot shower. I have to take lukewarm showers as otherwise I feel horrible. Even lukewarm showers my BG level can increase. I always try to take my showers in the evening as I am least affected and once in a while I can even drop a little.
This is really only a problem when I wash my hair and it’s a longer shower, a short quick shower at lukewarm water and I am fine, my BG then only goes up a little.