Whenever you get a grin on your face, your brain is releasing serotonin, the happy hormone. Smiling is the natural way to force your self to be happy. Many people even smile for five minutes straight in the morning to get themselves in a great mood for the day. It is a very powerful tool that is utilized less and less as we grow older and need happiness more than ever. 

Just remember that while happiness leads to smiles, smiles also lead to happiness. 

(50 Life Secrets and Tips)