Smiles are good for you and everyone around you. Not only do they make you appear more friendly, approachable and happy but they can make you live longer. Here's the scientific bit;
When you smile, your body releases endorphins, natural painkillers and serotonin. This process can boost your immune system and help to reduce ulcers, headaches, backaches, high blood pressure, mental problems, asthma and fatigue. So smile like you mean it :).