 Cryogen Spray Cooling spurt is applied to the skin surface immediately before laser exposure. As liquid cryogen rapidly evaporates, the superficial skin temperature is reduced as a result of supplying the latent heat of vaporization. Tetrafluoroethane, an environmentally compatible, non-toxic, non-flammable freon substitute, has been demonstrated in multiple studies to be a safe and effective cooling agent and is the only cryogenic compound currently approved for dermatologic use by the Food and Drug Administration. 