It is said laughter is the best medicine, but research has shown a sudden fit of the giggles could be bad for health, leaving some people literally in stitches.
A study of the reported benefits and damage of laughter in patients from 1946 to the present day found a loud guffaw can causing heart rupture, torn gullets and incontinence.
Researchers from Birmingham and Oxford universities concluded laughter can have serious health implications.
One woman with racing heart syndrome collapsed and died after a period of intense laughter and laughing 'fit to burst' was found to cause possible heart rupture or a torn gullet.
A quick intake of breath during laughing was also discovered to often cause inhalation of foreign bodies and can also provoke asthma attacks.
Bursts of laughter were also proven to cause incontinence and trigger hernias.
However the review found that chuckling can also have a positive impact in health.
Laughter reduces arterial wall stiffness, which researchers suggest may relieve tension. And it lowered the risk of heartattack.
Hospital clowns improved lung function in patients with chronic obstructive pulmonary disease and 'genuine laughter' for a whole day could burn 2000 calories and lower the blood sugar in diabetics.
Laughter also enhanced fertility: 36 per cent of would-be mothers who were entertained by a clown after IVF and embryo transfer became pregnant compared with 20 per cent in the control group.
The researchers say that their review challenges the view that laughter can only be beneficial but do add that humour in any form carries a "low risk of harm and may be beneficial".
They conclude that it remains to be seen whether "sick jokes make you ill, dry wit causes dehydration or jokes in bad taste cause dysgeusia (distortion of sense of taste)".
“We categorised the effects as beneficial or harmful, a usually clear-cut distinction. Some effects, however, such as lowering the threshold for seduction, could not be unequivocally categorised,” said the authors.
“Some readers may ignore the benefits of laughter. That would be serious. Others may dismiss its harms. We call them the laughing cavalier.”
The findings were reported in the BMJ Christmas edition.