Environment‐induced lentigines: formation of solar lentigines beyond ultraviolet radiation

There is no doubt that ultraviolet radiation ( UVR ) contributes to the generation of acquired lentigines in human skin, as indicated by the term solar lentigo. A growing number of recent epidemiological and mechanistic studies, however, strongly suggest that in addition to UVR , other environmental factors contribute to lentigines’ formation as well. We therefore here introduce the term ‘environment‐induced lentigo’ ( EIL ) to refer to acquired pigment spots of human skin. In this view point, we (i) summarize the existing evidence to support a role of environmental toxicants other than UVR in the pathogenesis of EIL s, (ii) we argue that activation of aryl hydrocarbon receptor ( AHR ) signalling by UVR and environmental toxicants is critically involved in triggering and sustaining a crosstalk between melanocytes, keratinocytes and fibroblasts, which then causes the development and persistence of EIL s in human skin, and (iii) we discuss clinical implications for the prevention and treatment of EIL s resulting from this concept.