For some people, when a conversation gets heated, so do their faces.
As explained in the SciShow video above, when something causes you instant stress, your nervous system may recognize this as a "threat," which activates a fight or flight response that affects your whole body.
This can cause your pupils to grow large, your heart to beat faster and your blood vessels to widen to increase blood flow. The blood vessels on your face also widen, and since they are close to the surface of the skin, it can create a noticeably rosy effect.
Anger isn't the only emotion that causes flushing: Nervousness or embarrassment can also cause the redness, as anyone who blushes easily already knows.
Want to learn more? Check out the video above.