The first reaction can be almost immediate: a sharp gasp, rapid breathing, an intense sensation of cold and a strong urge to get out. This is more than simple discomfort. Sudden exposure to very cold water triggers a series of automatic physiological responses. This is known as the cold shock response. It can affect breathing, heart function and blood pressure, particularly when exposure to cold is sudden. The first reaction may be a sudden gasp When the skin comes into sudden contact with very cold water, temperature-sensitive receptors send signals to the nervous system. The body responds by activating mechanisms designed to deal with the sudden thermal stress. One of the most noticeable responses is an involuntary gasp, often followed by rapid and deeper breathing, known as hyperventilation. This matters especially in water because losing control of breathing can make it harder to remain calm and maintain effective breathing. What happens to the heart and blood vessels? Cold shock a...