University of Michigan researchers have found that people who make more sweat while exercising are less prone to asthma than others.
Research leader Dr. Warren Lockette says that people who make less sweat, tears and saliva while exercising may have more breathing problems.
While the symptoms of "exercise-induced asthma" are similar to those of chronic asthma, people with the condition only develop attacks after several minutes of intense exercise.
Thought it is a common condition among trained athletes, its causes are poorly understood.
During the study, Lockette and his colleagues looked at 56 volunteers suspected of having the condition, measuring their responses to a drug called pilocarpine that induces sweat and saliva production, and another that constricts the airways in people with exercise-induced asthma.
The researchers observed that people showing the greatest response to the airway drug tended to have the lowest response to the sweating drug, and vice versa.
The group even tested the volunteers without the drug, and still found a correlation between the amount they sweated and the amount of saliva and tear secretion.
Lockette believes that low sweating might also mean less fluid in the airways.
"It now appears that how much fluid your airways secrete could be a key determinant in protecting you from exercise-induced asthma. So, if athletes sweat, drool, or cry, at least they won't gasp," the BBC quoted him as saying.
Leanne Male, from Asthma UK, said that the study was "interesting", but insisted that it was too early to say whether the research would lead to practical patient benefits..
"It is the first time that a link has been proposed between sweating, saliva production and the likelihood of experiencing exercise-induced asthma. However, it is far too early however to say whether or not this research is important for people with asthma, as currently it has generated nothing more than an interesting hypothesis which has yet to be substantiated," Leanne said.