It never occurred to me that there would be a scientific study specifically focused on laughter. And among the theories that attempt to explain humor and laughter, I think relief theory is the most plausible. Perhaps, this is where the term comic relief came about.
We usually tend to lean towards humor when we find comfort that whatever is disturbing, unusual or inconsistent is not necessarily dangerous. Oftentimes, we would find ways to express our sentiments we deem to be hurtful or uncertain in the form of a joke. Or we would retract the things we said that may have been taken in a different context with the remark: just kidding. Even the actual sharing of anecdotes or the use of sarcasm makes it plausible that it generates a sense of relief that it does not directly hit the point or that it did not happen to you. This actually leads me to the other theory which is superiority. Nevertheless, this is still in reference to relief.
Laughter is the free medicine we should all be taking in moderate dosages in our daily lives. After all, we all aspire for happiness in our temporal existence.