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If you've watched the musical Annie you may know that you're never fully dressed without a smile. There are a lot more reasons to smile than cosmetic ones, though. Turns out that smiles aren't just good for your looks. In fact, there is a lot of scientific evidence that proves smiling is good for your body and your mind, too.

Here are just a few ways that smiles make you happier and healthier:

Smiles lower stress

We've all heard the phrase "grin and bear it" and it turns out that there is scientific evidence to back it up. When you put a smile on your face, the movement of the facial muscles releases those naturally-occurring feel-good chemicals, endorphins. The small rush of endorphins trigger positive feelings and can lower stress levels and improve your mood. The smile doesn't even have to be real to be effective. One group of researchers found that fake smiles worked almost as well at reducing stress.

Smiling can make you feel happier in the short term

Once the muscles in our face pull into a smile, there is a positive feedback loop that goes back to the brain and reinforces our feeling of joy, according to Buffer. On a similar note, a study by a group at the University of Cardiff in Wales found that people who had Botox injections that made it impossible to frown ended up being happier on average than those who could frown. Not that we're encouraging Botox, as Mark Twain said, "Wrinkles should merely indicate where the smiles have been."

Smiling can reduce depression

Laughing and smiling encourages the release of serotonin, according to Dr. Isha Gupta, who spoke to NBC News. "Dopamine increases our feelings of happiness. Serotonin release is associated with reduced stress. Low levels of serotonin are associated with depression and aggression," says Dr. Gupta. "Low levels of dopamine are also associated with depression." Smiling can counteract that by increasing dopamine levels.

WATCH: This Foster Dog's Smiling Maternity Photo Shoot Is the Cutest Thing

Smiling can boost your immune system

Like endorphins, serotonin is a neurotransmitter that contributes to a person's happiness and wellbeing, Increased serotonin can make you more resistant to illness, by boosting the immune system. "What's crazy is that just the physical act of smiling can make a difference in building your immunity," Dr. Murray Grossan told NBC News. In fact, happiness in general has been shown to boost our body's resistance to disease.

Smiling is contagious

According to Psychology Today, a Swedish study, subjects were shown pictures of several emotions: joy, anger, fear, surprise, and a smiling face. When the researchers asked the subjects to frown, when they were looking at the smiling picture, they had a hard time not smiling back. It took a conscious effort to deliver a frown.

Smiling can be a thrill

The mere act of smiling can be a rush, according to research scientists who concluded "that smiling can be as stimulating as receiving up to 16,000 Pounds Sterling (that's over $20,000) in cash.

Smiling can reduce pain

Smiling not only offers a mood boost, but the cortisol and endorphins that are released when we smile can increase endurance, and believe it or not, reduce pain, Dr. Earlexia Norwood writes at the Henry Ford Health System blog. Apparently smiling through the pain is real!

Smiling can lower blood pressure

The cortisol and endorphins associated with smiling can also reduce your blood pressure and relax your heart rate, according to a study at the study by the University of Kansas. Once again, even fake smiles sufficed.

Smiling may make you live longer

Back in 1952, a group of researchers started following Major League Baseball players who had big grins on their baseball cards. They found that those smiling faces lived longer, around 79.9 years, compared to players who only partly smiled or didn't smile at all, who lived 5 to 7 years less.

Smiling can make for healthier marriages

When they compared yearbook photos of 21-year-old graduates with their situation later in life, they found that those who smiled with genuinely positive emotion had healthier marriages at age 52. "Those who smiled least, compared to those who smiled most, were actually five times more likely to be divorced at some point in their life," researcher Matthew J. Hertenstein said.

Smiling may make you happier

Another yearbook study, this one by psychologists at the University of California at Berkeley in 2001, found that women who grinned in their college yearbooks had better health, happier marriages, and expressed greater satisfaction in general with how their lives had turned out.

Any kind of smile – real or fake – can do a lot to lift your mood.

"There is something about making a smile that has a psychological impact," says Michael G. McKee, PhD, BCB, of Cleveland Clinic's Department of Psychology and Psychiatry. That's because "the inner smile and the outer smile potentiate each other," he explains. "If you're not feeling an inner smile, fake it outwards and it will increase the inner smile."