The Combined Human Exposure Model (CHEM) is a series of three modules designed to estimate aggregate exposure from consumer products. The first module is RPGen (Residential Population Generator). The second module is PUS (Product Use Scheduler). The third module is S2D (Source to Dose) which uses the outputs of the previous two diaries to determine the aggregate exposure for one simulated person per household over the course of a year. This is done by examining the various exposure pathways for each product used. While it was originally designed to only account for consumer products, further updates have added in simple algorithms for calculating exposure from both food and articles.  Performing these runs for a large population provides a distribution of expected exposures that can not only be used to estimate real life exposure for a similar population, but also reveal the most common pathways and can even be used to determine the kinds of traits and behaviors that correlate with the highest individual exposures.