Happiness Spreads Like the Flu

Happiness is contagious and spreads through social networks in much the same way the flu does, says a landmark new study that followed the fate of 4,700 people over 20 years. The research shows that a person's happiness can lift the mood of loved ones, neighbors, and even strangers with whom they don't have direct contact, the Washington Post reports. What's more, the ripple effect can last up to a year.

"You would think that your emotional state would depend on your own choices and actions and experience," said one of the researchers. "It also depends on the choices and actions and experiences of other people, including people to whom you are not directly connected. Happiness is contagious."