A cold bath is a moderate stimulus to the body. Cold water can quickly cool the body, help relieve muscle pain and stimulate the body's neuroendocrine. The body's response is to contract blood vessels, slow down blood flow, and accelerate metabolism to provide heat. The function of stimulating immunity comes from accelerating metabolism.

In addition, what is immunity? Immunity is the body's own defense mechanism, and it is the body's ability to identify and destroy any foreign body (virus, bacteria, etc.). Invade from the outside, deal with the aging, injury, death and degeneration of your own cells, identify and deal with mutant cells and virus-infected cells in your body.

There are two processes involved here: recognition (+memory) and killing. If the human body is properly stimulated in the process of "washing cold water", it can cause more recognition of the infringement and produce memory, which is helpful to improve immunity, but it is uncontrollable. How can we make the stimulation "just right" and not cause infection of other diseases and pathogens in the body because of external stimulation? It is impossible to require people of different constitutions according to uniform standards.

So my conclusion is: it is undeniable that taking a cold bath is good for us, but not everyone can always take it, such as girls in physiological period and the elderly.