Brain activity, and in particular which hemisphere is relatively more effective, is correlated with the dominant nostril (i.e., the nostril through which most of the air is exhaled when breathing through the nose). Thus, identifying which of the nostrils is dominant may have various applications. Described herein are systems and methods for identifying the dominant nostril. In one embodiment, a system includes at least one inward-facing head-mounted thermal camera (CAM) and a computer. The at least one CAM does not occlude any of the user's mouth and nostrils and is used to take thermal measurements of first and second regions below the right and left nostrils (THROI1 and THROI2, respectively). The computer identifies the dominant nostril based on THROI1 and THROI2. Optionally, the computer detects, utilizing THROI1 and THROI2, the three-dimensional (3D) shape of the exhale stream from at least one of the nostrils.