They grin, you bear it. Research reveals physical impact of a smile.

(University of Wisconsin-Madison) Research led by Jared Martin, a psychology graduate student at the University of Wisconsin-Madison, shows that smiles meant to convey dominance are associated with a physical reaction -- a spike in stress hormones -- in their targets. On the other hand, smiles intended as a reward, to reinforce behavior, appear to physically buffer recipients against stress.

from EurekAlert! - Social and Behavioral Science http://ift.tt/2F6vg9O