The exhaled air and volatile emission by the skin of human subjects were analyzed for traces of ethene (C2H4) by means of CO2 laser photoacoustic trace gas detection. Due to the extreme sensitivity of the detection system (6 part per trillion volume, 6:1012), these measurements could be performed on-line and noninvasively. Exhaled ethene was used as a biomarker for lipid peroxidation in the skin of human subjects exposed to ultraviolet (UV) radiation from a solarium. A change in the ethene concentration was already observed in the exhaled air after 2 min. Adaptation of the skin to UV exposure and direct skin emission could also be observed. © 1999 American Institute of Physics.