UV Index is a measure of the risk of suffering erythema by the long-term solar exposure. Mexico City is one of the most populated cities in the world, that due to its localization at about 2,245 m above sea level and intertropical latitude, tends to achieve high UV Index values all over the year. In the present study were analyzed around 2 millions of UV Index measurements along two decades (2000-2019), made by the Atmospheric Monitoring System of the Secretariat of the Environment of the Mexico City Government over Mexico City Metropolitan Area. The trend on monthly averages was of 0.64 % per year and the maximum UV Index values at solar noon ranging from 7 to 15. The exposure time, as the maximum limit to avoid sunburn, was also calculated for skin photypes I to VI, in the Fitzpatrick classification. The results may be useful to design preventive public health campaigns that target high risk groups with typical phototypes of the inhabitans of the Mexico City.