Abstract
Skin cooling is used to protect the epidermis in a variety of laser dermatology procedures, including leg vein treatment, hair removal, and port wine stain removal. Spray and contact cooling are the two most popular methods, but similarities and differences of these techniques are not well understood. A theoretical model of skin cooling is presented for two different regimens: "soft" cooling in which freezing of the skin is not permitted and "hard" cooling in which the skin can be frozen to a given depth. Spray and contact cooling were also compared experimentally using an in vitro model. For a fixed skin surface temperature, spray and contact cooling theoretically produce the same cooling profile in the skin. Anatomic depth of cooling depends on the time for which either the spray or contact is applied. In vitro experiments caused temperature at the simulated basal layer to be between -5 and +5 degrees C for both spray (tetrafluoroethane, boiling point -26 degrees C) and contact (-27 degrees C sapphire plate) cooling. The theoretical precooling analysis shows hard mode to be faster and more selective than soft mode; however, cooling time for hard mode must be carefully controlled to prevent irreversible epidermal damage caused by freezing. Both spray and contact cooling provide efficient skin cooling. The choice of cooling method depends on other factors such as the target depth, cost, safety, and ergonomic factors.
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