Therapies... - Hydrotherapy - Effects Of Hot And Cold Applications

The physiological effects of hot and cold water are dependent on the duration they are applied.

A short hot application on the skin, which lasts less than 5 minutes, produces a stimulatory response on circulation, as blood flow through the area is increased due to dilated blood vessels. In a long hot application, which is longer than 5 minutes, circulation is actually depressed as the movement of blood is decreased due to congestion produced by the first 5 minutes' exposure to heat.

In the incident of the short hot application the reaction of the body is considered to be an "intrinsic" response, where the reaction is a direct result of the heat, which is transferred to the body. In the long hot application, the response of the body is a "reactive" one, where your body creates a reflex as a result of its protective reaction to the hot application. This reflex in the body occurs to prevent the observation we made in the above paragraph that the peripheral circulation although individually small, is collectively large enough in its capacity to hold the blood of central circulation if it is diverted away from the heart.

In a short cold application, which is less than 1 minute, the effect is stimulating to the circulation, though this would initially seem to be contradictory. On its initial contact with the skin, the effect is immediately depressive as the blood vessels instinctively constrict. This momentary and brief vasoconstriction is important, but insignificant, since it is quickly followed by a vasodilation that last for 20 to 60 seconds

The "reactive" response of the body occurs to prevent serious instant vasoconstriction, which occurs in disorders such as Raynaud's disease. Subsequent longer applications of cold greater than 1 minute result again in vasoconstriction. In long cold applications of greater than 1 minute, the effect on the circulation is thus depressive -- an "intrinsic" response of the body to cold.