>>595899
Your body is defended against infection from white blood cells.
White blood cells are transported by the circulatory system.
In cold situation your blood vessels clamp down on circulation to prevent heat loss.
In stressful situation your intestines slow the circulation of blood.
Therefore in situation that is both cold and stressful, you have almost nil circulation of white blood cells, which leads to almost no protection from disease. And your spinal chord is in direct contact with the cold area (ass) and the stress circuited area (intestines) which are both full of all kinds of bacteria and diseases.
In a cold warfare scenario you could be perfectly hygienic, and get horribly sick without a scratch on you.