Objective: The aim of this review is to identify, critically evaluate, and summarize the laughter literature across a number of fields related to medicine and health care to assess to what extent laughter health-related benefits are currently supported by empirical evidence.
Data sources and study selection: A comprehensive laughter literature search was performed. A thorough search of the gray literature was also undertaken. A list of inclusion and exclusion criteria was identified.
Data extraction: It was necessary to distinguish between humor and laughter to assess health-related outcomes elicited by laughter only.
Data synthesis: Thematic analysis was applied to summarize laughter health-related outcomes, relationships, and general robustness.
Conclusions: Laughter has shown physiological, psychological, social, spiritual, and quality-of-life benefits. Adverse effects are very limited, and laughter is practically lacking in contraindications. Therapeutic efficacy of laughter is mainly derived from spontaneous laughter (triggered by external stimuli or positive emotions) and self-induced laughter (triggered by oneself at will), both occurring with or without humor. The brain is not able to distinguish between these types; therefore, it is assumed that similar benefits may be achieved with one or the other. Although there is not enough data to demonstrate that laughter is an all-around healing agent, this review concludes that there exists sufficient evidence to suggest that laughter has some positive, quantifiable effects on certain aspects of health. In this era of evidence-based medicine, it would be appropriate for laughter to be used as a complementary/alternative medicine in the prevention and treatment of illnesses, although further well-designed research is warranted.