Slightly above body temperature is preferred say 100 to 102. The following web site had this to say.
"To keep your good health, there are certain things you should know about maintaining the proper water temperature in your hot tub. The US Consumer Product Safety Commission recommends never allowing the temperature of the water in your hot tub to exceed 104ºF. Water temperatures over 110ºF have caused a number of deaths, according to their findings. They site that high water temperatures can cause drowsiness to occur that may lead to unconsciousness and drowning. The hot water will raise your body temperature, and thus your blood pressure, that may lead to heat stroke and death. They advise against pregnant women (since excessive water temperatures have a high potential for causing fetal damage during the early months of pregnancy) and young children (since their bodies do not get used to temperature changes as easily as adults do) using hot tubs before consulting a physician. Individuals suffering from obesity or having a medical history of heart disease, low or high blood pressure, circulatory system problems, or diabetes should also consult a physician before using a hot tub."
PS don't drink and soak!