Psychology
Why do humans blush, and what makes it unique?
Quick fact
Blushing occurs when adrenaline causes blood vessels in the face to dilate, increasing blood flow and reddening the skin—a response that only humans (and possibly some other primates) exhibit.
Why this is interesting
Blushing is a uniquely human response that makes your face flush with blood when you're embarrassed—and it's completely involuntary, controlled by the same nervous system that triggers your fight-or-flight response.