Staring at one side of the face increases blood flow on that side of the face.
To investigate the effect of observation on blushing, an experimenter sat next to 28 participants and looked closely at one cheek while the participant sang (embarrassing) or read aloud (not embarrassing). Increases in cheek temperature were greater on the observed than the unobserved side during both tasks. Changes in cheek temperature were symmetrical when the experimenter sat next to another 23 participants and looked straight ahead, as well as when the experimenter stared at one side of the participant's face through a glass window while the participant sang. However, increases in cutaneous blood flow were greater on the observed than the unobserved side of the forehead during singing. These findings suggest that staring at one side of the face triggers an ipsilateral increase in facial blood flow.