Now here's a thought to make you smile -- regardless of whether you're actually happy: Study subjects consistently underestimated the ages of smiling faces.German researchers had roughly 150 men and women of all age groups look at photos of people with various kinds of facial expressions -- angry, fearful, disgusted, happy, sad or neutral.The results: The observers were most likely to accurately guess the ages of blank-looking faces, but tended to underestimate the age of smilers by an average of two years.
 
Why might this be? There are certain age "cues" – crow’s feet, jowls, nasal labial folds (those lines that go from your nose to the edges of your mouth) which become more prominent as we age.Smiling moves the muscles and skin of the face in such a way as to "level the playing field" -- when we smile we all have crinkles around the eyes and creases around the lips (so called "parentheses") so the observer may simply read these as temporary wrinkles, unable to judge the extent of permanent wrinkles underneath.Another age cue: As the skin loses elasticity, the upper lip begins to sag downward, covering more of the upper teeth so that only the bottom teeth are visible.Smiling stretches this patch of skin horizontally, shortening it temporarily and thus mimicking the younger face.In addition, previous research has found that we're more likely to underestimate the ages of attractive people -- and observers perceive smiling faces as more attractive.
 
If this news is not incentive enough to flip your frown, then try hanging out with the happy crowd, as previous research found that contentment is contagious.Staying healthy will also help keep you happy, according to another study which found that fitness predicts happiness better than finances.Lifting weight can also lift your mood, while aerobic exercise boosts brain chemicals that provide a natural high.Beyond the beauty benefits of a buoyant expression, what you eat can directly affect your complexion -- for example, women with higher intakes of key complexion nutrients like vitamin C and omega-3 fatty acids tend to have fewer wrinkles.