231 Facial lentigines formation results from a complex interplay between solar ultraviolet radiation (sUVR) and ambient particulate matter (PM)

Chronic exposure to sUVR and, more recently, exposure to PM have been reported to be associated with more facial lentigines. In most urban environments, human skin is exposed to both environmental factors. In this epidemiological study we therefore assessed their combined effect on lentigines formation. We studied facial lentigines in 799 elderly Caucasian women (mean age 73.5 years) of the SALIA cohort using the SCINEXATM skin aging score. Long-term exposure to PM was estimated with land use regression models. Based on satellite data and data from the German Climate Center 5-year mean exposure to sUVR was calculated either as (i) daily UVB (290-315 nm) exposure based on the whole daylight period or as (ii) UV index based on the hour per day with maximal UV (290-400 nm). Associations between PM or sUVR with lentigines formation and the interactions PM*sUVR were estimated in single and multi-pollutant models. As expected sUVR exposure was associated with more lentigines on the cheeks (7.6% higher score on average; p=0.008) and this effect was only slightly attenuated when adjusting for PM. We also confirmed that PM was associated with more facial lentigines, and this association was still visible after adjusting for sUVR. We next observed that the association between sUVR and lentigines is affected by the level of PM. The sUVR effect was increasing at lower PM levels (e.g. UVBxPM10 p(interaction)=0.007), likely because sUVR was less shielded by PM in the troposphere. Of note, we also found that the association between PM and lentigines is modulated by the level of sUVR. At lower sUVR exposure, the PM effect on lentigines was stronger. All of these interactions indicated linear dose-responses. Thus, facial lentigines are the consequence of an interplay of at least two ubiquitous, environmental factors. It might take place in the troposphere and/or in the skin, where sUVR exposure might alter the response to PM.