Described herein are systems and methods for selecting a trigger of an allergic reaction. In one embodiment, a system includes an inward-facing head-mounted thermal camera (CAM) and a computer. CAM takes thermal measurements of a region on the nose (THN) of the user. Optionally, CAM weighs below 10 g and is located less than 15 cm from the user's face. The computer detects extents of the allergic reaction based on THN, receives indications of potential triggers of the allergic reaction to which the user was exposed, and selects the trigger, from among the potential triggers, based on the extents and the indications. Optionally, during most of the time the user was affected by the trigger, an effect of the trigger, as manifested via changes to THN, was higher than effects of most of the potential triggers.
