1. A system configured to detect a physiological response, comprising: an inward-facing head-mounted thermal camera (CAM in ) configured to take thermal measurements of a region of interest (TH ROI ) on a user's face; wherein CAM in does not occlude the region of interest (ROI) and is located less than 15 cm from the user's face; an outward-facing head-mounted thermal camera (CAM out ) configured to take thermal measurements of the environment (TH ENV ), and is located less than 15 cm from the face; and a computer configured to detect the physiological response based on TH ROI and TH ENV .