It happens. You're feeling down and need a quick pick-me-up. Or maybe you've found yourself in a silly argument you realize you'd like to get out of. You want to make things better in any little way you can, fast. What can you do?

Humans react almost instantly to the facial expressions we see in others. It takes just 30 milliseconds (thousandths of a second) for your brain to recognize and respond to others' emotional expressions, such as smiling or frowning.

Research shows that these reactions are unconscious, meaning that they're not even accessible to the conscious part of the brain, but rather are innate, unchangeable biological responses. We naturally mirror the facial expressions of the people we see.

So, when you smile at someone, he or she really can't help but smile back at you. (Even if it's more physiological than visible, it's there, according to measurement with some pretty fine-tuned instruments.)

SMILING MAKES US HAPPIER

What's more, studies have shown that the act of smiling has a profound impact on our emotional experience. Smiling triggers a reduction in stress-enhancing hormones and increases the production of mood-enhancing hormones. The same is true for frowning less: People who frown less report experiencing more positive feelings.

Fun fact: Some of this research is from anxiety and depression studies involving women who received frown-inhibiting Botox injections. Accounting for any change in their feelings of attractiveness, the women were found to be happier than they were when they were physically able to frown.

These results are explained by the facial-feedback hypothesis, which suggests that physiological responses, such as smiling or frowning, are not simply consequences of an emotion but also have a direct impact on that emotion. This hypothesis, first proposed by Charles Darwin, is key to understanding our own role in our emotions. If smiling can intensify feelings of pleasure and happiness and if frowning can amplify feelings of pain or sadness, we are clued into two simple ways of consciously acting to improve our emotional experience: smile more and frown less.

Another fun fact: If you smile while experiencing pain, your feelings of pain will be lessened. So, you might as well try smiling the next time you're experiencing something painful, like ripping off a particularly sticky band aid. (Ew/ouch!)

Even forcing a "fake" smile when you're not truly feeling it has been shown to reduce stress and result in more positive feelings. So, fake it 'til you make it.

And, if you can change your own mood through smiling, you can do the same for those around you. The facial feedback hypothesis also applies to interpersonal interaction, since, as we've learned, humans naturally mirror each others' facial expressions. By seeing others smile, we experience physiological changes that enhance our own feelings of happiness.

With the understanding that smiling makes people feel happier, whether you're the person making the smile or the person seeing it, and that smiling is contagious, we have a powerful tool to change our mood, our experience, and the world around us.

And, the icing on this cake: Smiling makes us healthier, too. Frequent, unabashed smiling has been shown to reduce blood pressure, improve the immune system, and may even reduce risk of chronic disease.

So, remember: Smiling will make you and those around you feel happier. In approximately 30 milliseconds.