Heat stress can affect many outdoor and indoor workers. To prevent heat-related illnesses (HRI) and injuries, employers should develop and use a comprehensive heat-related illness prevention program at the workplace. In occupational settings, heat stress is the combination of the heat your body produces (metabolic heat), environmental factors (for example, temperature and humidity), and clothing and personal protective equipment (PPE). While many workers need to wear PPE for protection from workplace chemical, physical, and biological hazards, PPE can increase the risk for HRIs.