Why do you burn calories in a sauna but not a tanning bed?

In a sauna, your body burns calories primarily due to the heat exposure, which raises your heart rate and stimulates your metabolism as your body works to cool itself down. This process can lead to increased calorie expenditure. In contrast, a tanning bed primarily emits ultraviolet (UV) light, which does not significantly raise your heart rate or induce the same metabolic response, resulting in minimal calorie burning. Thus, while both environments can lead to sweating, the physiological effects on calorie burning differ significantly.