Mitigating the urban heat island effect (UHIE) is a pressing need for sustainable urban design. A widely adopted strategy is to increase the solar reflectance (SR) of urban surfaces to limit solar heat gain. Recent advances have pushed SR to exceptionally high values. Still, these efforts are typically assessed using total SR alone, with little attention to how reflectance is redistributed across the solar spectrum, particularly in the ultraviolet (UV). Since UV radiation is a major environmental risk factor for skin cancer, this spectral shift introduced an overlooked health trade-off. Here, we unveiled and estimated the increased risk of skin cancer associated with high-SR UHIE mitigation materials. We quantified changes in erythemal weighted irradiance, annual erythemal radiant exposure, and skin cancer risk indicator to evaluate the impact of different UHIE mitigation strategies on skin cancer risk across locations. Our results identified pathways to mitigate UHIE while reducing skin cancer risk.