A Review of the Beneficial and Harmful Effects of Laughter
SOURCE: British Medical Journal 2013 (Dec 13); 347: f7274
R E Ferner, honorary professor of clinical pharmacology ,
J K Aronson, fellow 
ResearchChristmas 2013: Food For Thought Laughter and MIRTH (Methodical Investigation of Risibility, Therapeutic and Harmful): Narrative Synthesis
Every December, the BMJ publishes hilarious Christmas research.
Their 2013 offerings are now online at:
Objective To review the beneficial and harmful effects of laughter.
Design Narrative synthesis.
Data sources and review methods We searched Medline (1946 to June 2013) and Embase (1974 to June 2013) for reports of benefits or harms from laughter in humans, and counted the number of papers in each category.
Results Benefits of laughter include reduced anger, anxiety, depression, and stress; reduced tension (psychological and cardiovascular); increased pain threshold; reduced risk of myocardial infarction (presumably requiring hearty laughter); improved lung function; increased energy expenditure; and reduced blood glucose concentration.
However, laughter is no joke — dangers include syncope, cardiac and oesophageal rupture, and protrusion of abdominal hernias (from side splitting laughter or laughing fit to burst), asthma attacks, interlobular emphysema, cataplexy, headaches, jaw dislocation, and stress incontinence (from laughing like a drain). Infectious laughter can disseminate real infection, which is potentially preventable by laughing up your sleeve. As a side effect of our search for side effects, we also list pathological causes of laughter, among them epilepsy (gelastic seizures), cerebral tumours, Angelman’s syndrome, strokes, multiple sclerosis, and amyotrophic lateral sclerosis or motor neuron disease.
Conclusions Laughter is not purely beneficial. The harms it can cause are immediate and dose related, the risks being highest for Homeric (uncontrollable) laughter. The benefit-harm balance is probably favourable. It remains to be seen whether sick jokes make you ill or jokes in bad taste cause dysgeusia, and whether our views on comedians stand up to further scrutiny.
— Robert Burton, The Anatomy of Melancholy (1621)
The BMJ has not dealt seriously with laughter since 1899, when an editorialist, following an Italian correspondent’s suggestion that telling jokes could treat bronchitis, proposed the term “gelototherapy” (in Greek gelōs means laughter; in Italian gelato means ice cream).  The journal had, a year before, described heart failure following prolonged laughter in a 13 year old girl.