People say a smile is contagious. Once you start smiling around someone, he or she just seems to automatically smile too! In physiological terms, a smile is a facial expression formed by flexing the muscles most notably near both ends of the mouth. Speaking subjectively, the smile can be also around the eyes. Smiling is customarily an expression of pleasure, happiness, or amusement. However, it can also be an involuntary expression of anxiety, in which case it can be known as a grimace. There is much evidence that smiling is a normal reaction to certain stimuli and occurs regardless of culture.

Laughter is an audible expression or appearance of merriment or amusement or an inward feeling of joy and pleasure (laughing on the inside). It may be triggered by jokes, tickling, or other things. Inhaling nitrous oxide can also induce episodes of strong laughter.
Laughter is a part of human behavior regulated by the brain. It helps humans clarify their intentions in social interaction and provides an emotional context to conversations. Laughter is used as a signal for being part of a group – it signals acceptance and positive interactions with others. Laughter is sometimes seemingly contagious, and the laughter of one person can itself provoke laughter from others. This may account in part for the popularity of laugh tracks in situation comedy television shows, also known as sitcoms. A laugh track is an artificial sound of audience laughter.
Without smiling and laughter, we would see a totally different world altogether. There have been short time periods when certain groups of people in different parts of the world have constantly faced hard times and they have hardly ever experienced laughter, so just imagine how the whole world would be if no one ever had a chance to smile or laugh! Smiling and laughing are two things that actually help us make it through each day. We smile because we have hope, because we did a great job at an assigned task, or because we want to encourage someone else.
Studies have shown that patients who smile and/or laugh while they are sick actually recover faster than patients who do neither. When you smile and laugh, your brain sends signals to your body that let it know that you are well.
According to behavior change expert Mark Stibich Ph.D, here are the top ten reasons to smile:
1. Smiling makes us attractive.
We attract positive minded people when we smile often.
2. Smiling improves our mood.
The more you smile, the more your brain sends signals to your body that say that you are feeling well.
3. Smiling is contagious.
Like I mentioned earlier, the more you smile, the more people around you will smile too.
4. Smiling relieves stress.
Having a bad day? Try thinking about something good in your life, and you will most likely smile about it and not feel so stressed.
5. Smiling boosts your immune system.
Smiling helps the immune system to work better. When you smile, immune function improves possibly because you are more relaxed. Prevent the flu and colds by smiling.
6. Smiling lowers your blood pressure.
When you smile, there is a measurable reduction in your blood pressure. Give it a try if you have a blood pressure monitor at home. Sit for a few minutes, take a reading. Then smile for a minute and take another reading while still smiling. Do you notice a difference?
7. Smiling releases endorphins, natural pain killers and serotonin.
Studies have shown that smiling releases endorphins, natural pain killers, and serotonin. Together these three make us feel good. Smiling is a natural drug.
8. Smiling lifts the face and makes you look younger.
People who smile a great deal, tend to have less lines and wrinkles on their faces than people who don’t smile as much or frown too often.
9. Smiling makes you seem successful.
Smiling people appear more confident, are more likely to be promoted, and more likely to be approached. Put on a smile at meetings and appointments and people will react to you differently.
10. Smiling helps you stay positive.
Try this test: Smile. Now try to think of something negative without losing the smile. It’s hard. When we smile our body is sending the rest of us a message that “Life is Good!” Stay away from depression, stress and worry by smiling.