Research suggests smiling doesn't just spread sunshine; it strongly affects your mood.
In February 2009, psychologists at the University of Cardiff in Wales found that people whose frown muscles were deadened by Botox were happier and less anxious than those who hadn't had the wrinkle treatment. Another study, appearing in the May 2008 issue of the Journal of Pain, revealed that people who grimace during uncomfortable procedures feel more pain than those who don't.
But a 2005 study by Hewlett Packard and the British Dental Health Foundation was perhaps the most intriguing. Researchers measuring brain and heart activity found that volunteers were as stimulated by imagining someone they loved smiling at them as they were by being told they'd won a cash prize. David Lewis, a psychologist and director of research at Mindlab International in Brighton, England, which conducted the study, says a warm smile can create a "halo" effect, helping us "feel more optimistic, more positive, and more motivated."