Your pupils change size as you breathe

The size of our pupils fluctuates as we breathe. They are at their smallest as we start to breathe in, increase steadily to reach their largest size when we are in the middle of breathing out, then shrink rapidly as we finish exhaling.

“I haven’t tried to see it with my naked eye,” says Martin Schaefer at the Karolinska Institute in Stockholm, Sweden. “I think it would be difficult to see.”

The fact that breathing can affect pupil size has been known for decades, but all the scientific…