The three-dimensional (3D) shape of the exhale stream from a user's nostrils is often correlated with the user's state (e.g., an emotional state and/or a certain health condition). Thus, identifying the shape of a user's exhale stream can help determine the user's state. In one embodiment, a system that selects a state of a user includes at least one inward-facing head-mounted thermal camera that takes thermal measurements of at least three regions below the nostrils (THS). THS are indicative of shape of the exhale stream (SHAPE). The system also includes a computer that generates feature values based on THS, which are indicative of the SHAPE, and utilizes a model to select the state of the user, from among potential states of the user, based on the feature values. Optionally, the system includes a user interface that present the user's selected state.
