Scientific evidence suggests being happy may boost our immune system. Sheldon Cohen and his colleagues (2003) found people who were happy, lively, calm, or exhibited other positive emotions like optimism, were less likely to become ill when exposed to a cold virus than those who reported fewer of these emotions. They also found that when happy people did come down with a cold, they had fewer symptoms. A 2006 study by Cohen had the same result: people who reported positive emotions were less likely to catch colds and were also less likely to report symptoms when they did get sick.