[2] Most commonly, it is considered an auditory expression of a number of positive emotional states, such as joy, mirth, happiness or relief.
On some occasions, however, it may be caused by contrary emotional states such as embarrassment, surprise, or confusion such as nervous laughter or courtesy laugh.
Other than humans, some other species of primate (chimpanzees, gorillas and orangutans) show laughter-like vocalizations in response to physical contact such as wrestling, play chasing or tickling.
One group of researchers speculated that noises from infants as early as 16 days old may be vocal laughing sounds or laughter.
[20] Laughter also boosts the number of antibody-producing cells and enhances the effectiveness of T-cells, leading to a stronger immune system.
[22] Anecdotally, journalist and author Norman Cousins developed in 1964 a treatment program for his ankylosing spondylitis and collagen disease consisting of large doses of Vitamin C alongside laughter induced by comic films, including those of the Marx Brothers.
"I made the joyous discovery that ten minutes of genuine belly laughter had an anesthetic effect and would give me at least two hours of pain-free sleep," he reported.
"When the pain-killing effect of the laughter wore off, we would switch on the motion picture projector again and not infrequently, it would lead to another pain-free interval.
[25] Working with recorded interactions, researchers have created detailed transcripts that indicate not only the presence of laughter but also features of its production and placement.
Contrary to notions that it is spontaneous and involuntary, research documents that laughter is sequentially organized and precisely placed relative to surrounding talk.
More than simply an external behavior "caused" by an inner state, laughter is highly communicative and helps accomplish actions and regulate relationships.
Philosopher John Morreall theorizes that human laughter may have its biological origins as a kind of shared expression of relief at the passing of danger.
Friedrich Nietzsche, by contrast, suggested laughter to be a reaction to the sense of existential loneliness and mortality that only humans feel.
In addition, the extent of the inconsistency (and aspects of its timing and rhythm) has to do with the amount of danger the audience feels, and how hard or long they laugh.
Although most people find it unpleasant, being tickled often causes heavy laughter, thought to be an (often uncontrollable) reflex of the body.
Normal note durations with unusually long or short "inter-note intervals" do not happen due to the result of the limitations of our vocal cords.
Unpleasant laughter spells, or "sham mirth", usually occur in people who have a neurological condition, including patients with pseudobulbar palsy, multiple sclerosis and Parkinson's disease.
[34] Some of the emotional benefits include diminishing anxiety or fear, improving overall mood, and adding joy to one's life.
[35] Laughter therapy also has some social benefits, such as strengthening relationships, improving teamwork and reducing conflicts, and making oneself more attractive to others.
Therefore, whether a person is trying to cope with a terminal illness or just trying to manage their stress or anxiety levels, laughter therapy can be a significant enhancement to their life.
In another survey, researchers looked at how Occupational Therapists and other care givers viewed and used humor with patients as a means of therapy.
It did suggest that additional research was still needed since "well-designed randomized controlled trials have not been conducted to date validating the therapeutic efficacy of laughter.
"[38] In 2017, an institution in Japan conducted an open-label randomized controlled trial to evaluate the effects of laughter therapy on quality of life in patients with cancer.
A 1999 study by two humor researchers asked 80 people to keep a daily laughter record, and found they laughed an average of 18 times per day.
"[citation needed] Philosopher Arthur Schopenhauer devotes the 13th chapter of the first part of his major work, The World as Will and Representation, to laughter.
[48] One of the theories of the essay is that laughter, as a collective activity, has a social and moral role, in forcing people to eliminate their vices.
[52] Several non-human species including rats, apes and dolphins demonstrate vocalizations that sound similar to human laughter.