In laser dermatologic surgery, cryogen spray cooling (CSC) is used to avoid laith damage such as scars from skin burning due to the melanin absorption of the laser beam. As the cryogen is fully atomized from the nozzle, evaporation of the droplets may quickly drop the cryogen temperature below −60 °C, depending on the spray distance from the nozzle. Such a low temperature is potential to cold injury for skin. Therefore, spray process should be accurately controlled during clinical practice to achieve sufficient protection and to avoid cold injury. This study presents a numerical analysis of cold injury of skin in cryogen spray cooling for dermatologic laser surgery. The model for cryogen spray cooling of skin, developed early, is extended to include the freezing of skin cells. The model predictions include the movement of the lethal isothermals. The severity of cold injury is then quantified under various clinical conditions. The effect of initial temperature and the spurt duration on possible cold injury of skin are also investigated.

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