Cryogen spray cooling of skin surface with millisecond cryogen spurts is an effective method for establishing a controlled temperature distribution in tissue and protecting the epidermis from nonspecific thermal injury during laser mediated dermatological procedures. Control of humidity level, spraying distance and cryogen boiling point is material to the resulting surface temperature. Decreasing the ambient humidity level results in less ice formation on the skin surface without altering the surface temperature during the cryogen spurt. For a particular delivery nozzle, increasing the spraying distance to 85 millimeters lowers the surface temperature. The methodology comprises establishing a controlled humidity level in the theater of operation of the irradiation site of the biological tissues before and/or during the cryogenic spray cooling of the biological tissue. At cold temperatures calibration was achieved by mounting a thermistor on a thermoelectric cooler. The thermal electric cooler was cooled from from 20.degree. C. to about -20.degree. C. while measuring its infrared emission.
Part of this invention was made with Government support under grants from the National Science Foundation, BES-9634110, the Whitaker Foundation 96-0235, the Institute of Heart, Lung and Blood 1R154HL58215-01 and the Institute of Arthritis and Musculoskeletal and Skin Disease 1R29-AR41638-01A1, R15-AR43403-01, and IR01-AR42437-01A1 of the National Institutes of Health. This invention was also made with Government support under Grant DE-FG03-91ER61227, awarded by the Department of Energy. The Government has certain rights thereto.