From the Grinch to the Scrooge, the yuletide holiday loves a morose figure. Now, a review of medical studies in The Lancet appears to show the downsides to… laughter. Investigators from the United Kingdom conducted standard searches to review the literature since the 1946 on “the benefits or harms from laughter in humans.”

Drawing on the magic of modern science, they found some 5,000 studies touching on laughter, prompting them to conclude: It’s not all good. Titterings aside, the force of raucous laughing-out-loud may dislocate jaws, trigger asthma attacks, and pop hernias. The physiological response to mirth might also kickstart Pilgaard-Dahl and Boerhaave’s syndromes, rare but dastardly conditions known to man.

“Laughter is not purely beneficial,” the investigators wrote. “The harms it can cause are immediate and dose-related, the risks highests for [uncontrollable] laughter. The benefit-harm balance is probably favorable. 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.”

The purported benefits of laughter paled by comparison, however. Among possible benefits cited by previous study included “reduced anger, anxiety, depression, and stress. Laughter also brought an increased tolerance for pain, lowered risk of myocardial infarction, improved lung function, increased energy expenditure, and reduced blood glucose concentration.

“However, laughter is no joke,” the investigators wrote. Dangers include increased risk of cardiac and oesophageal rupture, asthma attacks, interlobular emphysema, cataplexy, headaches, jaw dislocation, and popped hernias.

Using standard review tools, the investigators also found pathological causes of laughter, which include epilepsy, cerebral tumors, Angelman’s syndrome, strokes, multiple sclerosis, and amyotrophic lateral sclerosis. It was all so clear.

“Our review refutes the proposition that laughter can only be beneficial,” the investigators wrote. They added that the relatively low health risks posed by laughter, conversely, shouldn’t make a difference either.

Source: Ferner, R.E. Laugher And MIRTH (Methodical Investigation Of Risibility, Therapeutic And Harmful): Narrative Synthesis. The Lancet. 2013.