One reason for the popularity of saunas is the fact that they strengthen your immune system. By using a sauna regularly and correctly – i.e., alternating between hot and cold – you can train your body to adapt better to sudden changes in temperature between indoors and outdoors, and not get cold so quickly. Every time you use a sauna, you’re reinforcing your body’s defence mechanisms. The heat inside the sauna raises your core body temperature by 1°-2°C. This is like having an artificial fever, and all the cells in your body react accordingly. But the healthful effect of the sauna is not complete without the body cooling process which immediately follows – the complete cycle of alternating between hot and cold, in other words. Because only by using the sauna correctly and regularly can you strengthen your immune system.