People who have "learned" to always smile at work, where "customer-friendly" behavior is required, are immediately noticeable. They are betrayed by a forced, tense and extremely unnatural smile. This is visible immediately, and does not cause any positive emotions.
Why is a sincere and open smile so useful?
First of all, its benefits are associated with socialization. A smiling person does not experience communication problems, he has more friends and good acquaintances. Even if you are melancholic by nature, don't forget to smile more often! But this is not the only reason.
Smiling is a natural way to increase the production of endorphins, the action of which has a beneficial effect on a person’s mood.
All the same endorphins, combined with a good mood, are an excellent “recipe” for strengthening immunity. Smile more often, and you will be less likely to experience colds! It has also been observed that smiling, accompanied by the release of a large amount of endorphins, helps people fight pain.

P.S. I want to find a relationship here!