I found the following article on the web about hot showers affecting BG.
“8 Things That Affect Your Blood Glucose Levels
2. Heat - A hot day, or even a shower or bath that is too hot will affect your sugars. Heat can cause your sugar levels to fluctuate. According to the Mayo Clinic, diabetics often have damage of the sweat glands affecting the body’s ability to cool down. Dehydration can be a result of a hot day, as well as a result of high blood glucose levels. High levels cause the body to excrete more urine, causing dehydration if one does not increase their intake of caffeine free fluids like water, seltzer, and sugar-free drinks. Heat can cause dehydration as well and could result in the more serious affects of heat exhaustion. Remember, try to keep out of the direct sunlight on a hot day, drink lots of fluids, exercise in the cool of the morning or late evening. You may find, like me, that you just cannot take the heat like you did before the diabetes.”