Environmental factors, such as aging and thermal stress, can seriously impact the electromagnetic compatibility behavior of an integrated circuit (IC). The standardized IC emission model for conducted emission (ICEM-CE) and IC immunity model for conducted immunity (ICIM-CI) can be used in industry to predict electromagnetic behavior at the IC and the printed circuit board level. However, these do not take into account the effect of aging and extreme temperature variations. In this article, a custom IC designed in silicon-on-insulator technology, containing several independent analog blocks, is used to characterize the influence of aging and temperature on conducted emission and immunity through measurements and transistor-level simulations. The highly accelerated temperature and humidity stress test (HAST) was performed to evaluate aging and its influence on IC parameters. The results show that the passive distribution network is only influenced by thermal stress and not HAST aging. The latter mainly affects the active elements in the IC and reduces the conducted emission and immunity levels through intrinsic permanent degradation mechanisms. Furthermore, thermal stress mainly causes drifts in the transistor characteristics (such as threshold voltage and effective mobility), which affect the conducted emission and immunity levels and resulting in soft failures. All drifts/tolerances collected from measurements and simulations are characterized in a way that makes it possible to include them in potential future versions of the ICEM-CE and ICIM-CI standards.