Feeling happy? Go ahead and smile — but know that you may be telling others more about yourself than you think.
The meaning of a smile changes depending on the social context, studies show. Some smiles bring benefits, but others reveal hidden weakness. Humans smile more depending on who they're talking to, and those smiles can hint at their futures.
Without further ado, here are five things your smile tells others about you.
1. Will your marriage last?
Wedded bliss may be linked to an easy grin. According to a study published in 2009 in the journal Motivation and Emotion, the way people smile in old photographs predicts their later success in marriage.
In one study, psychologists rated people's college yearbook photos for smile intensity (muscle stretching around the mouth and eyes). They found that none of the biggest grinners divorced later in life. In comparison, 25 percent of the most straight-faced experienced divorce.
A second study of childhood photos of people over age 65 found a similar link. Among those with the biggest smiles in the childhood pictures, 11 percent later experienced divorce, compared with 31 percent of the least smiley.
A bigger smile may reflect a happy-go-lucky approach to life, the researchers reported. Or bigger smiles may attract a happier partner, and lead to a happier relationship.
2. How fertile are you?
A healthy smile can reflect your overall health, multiple studies show. For women, smiles can even reveal fertility.
Women with gum disease take an average of two months longer to conceive than women without, according to research published in 2009 in the journal Obstetrics and Gynecology. Gum disease is linked to an increased risk of heart disease, Type 2 diabetes, respiratory disease and kidney disease. The link appears related to increased inflammation that accompanies gum disease, the researchers found.
3. How much earning power do you have?
A teenager's grin can predict how much cash he or she will rake in as an adult. According to a study published in 2012 in the journal Proceedings of the National Academy of Sciences, happy teens earned 10 percent more income than average at age 29, while gloomy adolescents earned 30 percent less than average at that age.
Happiness is likely linked with fewer worries and less stress, study researchers reported. Less worry means more mental space to focus on job-related tasks.
4. How powerful are you?
Smiles aren't just about happiness. They're also a sign of social status. A 1998 study in the journal Personality and Social Psychology Bulletin found that high-powered people, as well as people interacting with others of equal power, smiled when they felt happy.
In contrast, people with less social power than the person they were interacting with smiled regardless of their own emotions.
The findings suggest that powerful people have the privilege of smiling when they please, whereas those with less power are obligated to smile in order to ingratiate themselves. [5 Surprising Ways to Banish Bad Breath]
5. How good a fighter are you?
The link between smiles and power holds in the physical realm, as well. In one study, professional mixed martial arts fighters who grinned in photographs taken the day before a match were more likely to lose than fighters who presented a tough mug for the camera.
Fighting is about dominance, and smiles may inadvertently signal that a person is less dominant, hostile or aggressive, researchers reported online Jan. 28, 2013, in the journal Emotion.
Even untrained observers caught on to the message in the smiles, the same study found. People viewed a fighter as more trustworthy and agreeable, but less aggressive and less physically dominant, if they saw him smiling versus posing with a neutral expression.
The takeaway? Smiles grease the social wheels in most situations, and happiness is usually a boon. But if you're going head-to-head in a contest of dominance, put your game face on.
Live Science newsletter
Stay up to date on the latest science news by signing up for our Essentials newsletter.
Stephanie Pappas is a contributing writer for Live Science, covering topics ranging from geoscience to archaeology to the human brain and behavior. She was previously a senior writer for Live Science but is now a freelancer based in Denver, Colorado, and regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor's degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz.