The immune system is a fiercely complicated partnership of various cells in the human body. Many people have noticed that cold training enhances their immune system. A stronger immune system reduces a person’s chances of catching a cold or experiencing flu-like symptoms. So far, we have not uncovered the scientific basis for the enhancement of the immune system through cold exposure. This is in part due to the dazzling complexity of the immune system. What we do know, however, is that cold training, especially in combination with our breathing exercises, can affect a wide range of physiological processes. These include the blood oxygen level, pH-level and Co2 level. These changes bring about a hormonal reaction, which in turn affects many other physiological processes (e.g. energy management, immune system, sleep cycle, stress). This could explain why cold training can boost the human immune system.