SAN DIEGO -- More than half of people with asthma report that their symptoms are brought on by laughter, according to a study to be presented at the American Thoracic Society International Conference on May 24.

The study of 235 patients with asthma found that 56% had laughter-induced asthma (LIA). Asthma that is triggered by laughter doesn't seem to cause more asthma flare-ups requiring emergency room visits or hospitalizations compared with other types of asthma, according to study author Stuart Garay, M.D., Clinical Professor of Medicine at NYU Medical Center in New York. "But patients did report that during times when their asthma is well controlled they can laugh for longer without getting asthma symptoms. That suggests that laughter-induced asthma may be a sign that a person's asthma isn't as well controlled as it could be. People with asthma should be allowed to laugh."

Nobody knows how laughter brings on asthma, but it might involve hyperventilating, Dr. Garay said. He noted that exercise was the only trigger more common in people with laughter-induced asthma compared with asthma not induced by laughter (61% of people with LIA vs. 35% of asthma patients without LIA).

Dr. Garay was struck by how common laughter-induced asthma is. "It's as common as some of the most well-known asthma triggers, such as grasses, trees, pollen, fumes and odors, and it's even more common than dust mites, allergy to animals and molds," he said. "It's a little-appreciated frequent trigger."

The study found that the most common symptom in patients with laughter-induced asthma was coughing, which generally starts within two minutes. The next most common symptom was chest tightness.

How much laughter can set off breathing problems? "It depends on the patient," Dr. Garay said. "For a majority of patients, mild laughter or even a chuckle will set off coughing. For others, laughing hard will bring on asthma symptoms."

