Skin thermal recovery following cryotherapy: a comparison of liquid nitrogen and liquid nitrous oxide

Cryotherapy is a common technique used in the management of superficial skin lesions, with current advice on the correct timing for freeze-thaw cycles based on nonscientific visual skin appearances. We investigated the effect of cryotherapy on thermal thawing times by creating a porcine skin model in a laboratory setting maintained at normal skin temperature and comparing liquid nitrogen and liquid nitrous oxide. Thermal assessment was performed using a thermal camera attached to an iPhone 11Pro (R) smartphone. Liquid nitrogen reduced skin temperature to -60 degrees C after 5 s of application, recovering to 0 degrees C after 70 s. Liquid nitrous oxide reduced skin temperature to -34.8 degrees C after 5 s but had a faster recovery to 0 degrees C after only 20 s. Both cryogens required a thawing period of 5 min to recover to normal skin temperature. We therefore suggest that optimum cellular degradation should allow for 5-min freeze-thaw cryotherapy cycles; a slower thawing period than is in current common practice. This study investigated the effect of cryotherapy on skin temperature, specifically looking at the extent of the isotherm and the recovery time to reach normal skin temperature. Both liquid nitrogen and liquid nitrous oxide were found to have a thawing period of 5 min to normal skin temperature. We suggest that optimum cellular degradation should allow for 5-min freeze-thaw cryotherapy cycles; a slower thawing period than is in current common practice.