We all have friends or family who fit the polar ends of personality—the cheerleader types who can smile even after getting puddle-pummeled by a bus and the negative types who frown at butterflies.Positive emotions play a crucial role in developing the enduring relationships that are critical for our happiness. One example is the boomerang smile—a shared smile between a mother and baby.We know negative emotions change our brain function to increase stress, which increases health risks such as cancer and heart disease. Since we also know positive emotions change the way brains function to reduce stress, they can help cancel out those health risks.MORE: Train Yourself to Be HappierThe best evidence comes from studies on meditation and relaxation therapies, which show their ability to calm a jumpy heart. Other studies have found a correlation between positive moods and the improvement of physical symptoms such as listlessness and weakened immune function. All are clearly contributors to happiness (or lack thereof).Part of the reason happiness is an important part of being beautiful is that you can’t really feel happy unless your body feels tuned and your mind feels sharp. Without a sound body you can’t be of sound mind.Almost every study of longevity indicates one secret that makes people healthier and happier: helping others. Some research shows a 60 percent decrease in mortality figures among those who help others; they’re aided by what’s called the “helper’s high.”RELATED RESEARCH: Do Good, Feel HappierSpecifically, it’s the dignity, the joy, the passion and the purpose of helping others that create these beneficial effects. Research shows that people who donate money are happier than people with the same amount of money who don’t donate to others.Helping others inspires gratitude for what life has given you and helps you define your own purpose in life. After all, the real secret may be realizing that true peace isn’t about happy, giddy and feeling as if you’re charged up on Red Bull all the time. It’s about slowing down enough to realize that you have a lot of gifts—gifts that you should be passing along to others.QUIZ: How Happy Are You?