Skin cancer is a medical condition that is becoming more common in many countries as a result of excessive exposure of individuals to sunlight. The ultraviolet range of the electromagnetic radiation is responsible for 90% of the cases involving the development of melanomas. Additional factors like the skin tone and texture can increase the risk of radiation exposure when the water content retained by the skin starts to drop dramatically. In this paper we present a small, batteryless wearable device that combines the computation of sunlight exposure with the measurement of the impedance of the skin and temperature, at any time of the day and independently of the location of the person wearing the sensor. Results have shown a good performance in tracking the ultraviolet index and the variation of impedance for different levels of skin hydration.