Cold exposure works in several ways:
Stress Inoculation: Cold exposure can be used as a form of stress inoculation, helping to raise your stress threshold and tolerate heightened levels of real-life stress. This is achieved by suppressing the activation of the sympathetic nervous system, which is the alertness or stress system.
Fat Loss and Thermogenesis: Cold exposure can also be used for fat loss and thermogenesis. When you shiver in response to cold, your body releases a chemical called succinate from your muscles. This chemical activates a particular category of fat called brown fat, which is rich with mitochondria and generates heat in the body. This process increases metabolism and causes fat burning.
Release of Norepinephrine: Deliberate cold exposure is a potent stimulus for the release of norepinephrine in the brain and body. There are neurons within your skin that sense cold and other neurons that can directly release norepinephrine into the fat stores, causing white fat cells to convert to beige and brown fat.
Potential Increase in Testosterone: Some people use deliberate cold exposure to the groin, particularly the testicles, to try and increase testosterone. While there are no specific well-controlled studies that show this works, it's plausible that the increase in dopamine caused by cold exposure could stimulate testosterone indirectly.
Remember, everyone's response to cold exposure can vary, and there's no right or wrong way to go about