Tears,of course,are necessary to protect the eyes and keep them moist.When faced with extreme emotions such as sadness,anger or even happiness,we cry,said Sage Timberline,a pediatrician at the University of California,Davis,Children's Hospital in Sacramento,California.That temporary stress triggers a fight-or-flight response,which produces tears to further protect the eye.These emotional tears can also help release stress-inducing hormones that may have been building up during tough times;this contributes to that sense of relief that follows a good cry,she told Live Science.