A study at Harvard Medical School released in December found that happiness spreads through social networks in amazing ways.  One happy person can trigger a happy reaction in a friend who can trigger a happy reaction in another friend, who can trigger another happy reaction in another friend, who (you guessed it) can trigger another happy reaction in yet another friend. In all, this chain reaction can spread three degrees away from the original happy person.

The influence is not only on friends.  Family members and even neighbors catch it, too.  And what’s even more amazing is that this joyous effect can last up to one whole year!

Here’s another finding of the study:  unhappiness is not as powerful as happiness.  Sad feelings do not spread as efficiently as joyful ones.

The study analyzed data from nearly 5,000 people and found that friends, families, and even neighbors can influence each other in ways that spread to indirect relationships-your happiness can influence your neighbor and her friends, her friends’ friends, and their friends’ friends’ friends.

What are some practical implications for those of us who seek to maximize our happiness?  That’s right, hang out with happy people and their friends.  And be aware that your mood can influence others far removed from you.