<qa>  What is the only cryogenic compound currently approved for dermatologic use?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. 