Air pollution could raise risk of appendicitis, it has been found.
A University of Calgary team found more patients were hospitalised on days when pollution levels were at their highest.
The study, presented to an American College of Gastroenterology conference, suggests pollution raises the general risk of tissue inflammation.
If the appendix becomes inflammed it must be removed surgically to avoid the risk that it will burst, and put the patient's life at risk.
The appendix is a small pouch connected to the large intestine. Its role is unclear, but there is some evidence to suggest it may harbour beneficial bacteria that aid digestion and fight infection.
Appendicitis, which causes the appendix to swell up and fill with pus, can be caused by infection or obstruction, but in many cases there is no obvious cause.
The Calgary team identified more than 45,000 adults who were hospitalised for appendicitis between 1999 and 2006.
They found patients were approximately 15% more likely to be hospitalised on days of highest ozone concentrations compared to days of lowest ozone concentrations.
Similar findings were seen for other pollutants such as sulphur dioxide, nitrogen dioxide, and particulate matter - although the effect appeared to be not as marked.
The effect of air pollution was strongest during the summer months, when people were more likely to be outside.
Previous studies have shown that air pollution may promote other disease states through inflammation, and the researchers said this was the most likely explanation for their finding.
Lead researcher Dr Gilaad Kaplan said: "If the relationship between air pollution and appendicitis is confirmed, then improving air quality may prevent the occurrence of appendicitis in some individuals."
Dr Anton Emmanuel, medical director of the digestive disorders charity Core, said it was possible that air pollution had an impact on blood flow in the gut which in theory could make obstruction of the neck of the appendix more likely.
However, he said any impact was likely to be more longer term, with prolonged periods of air pollution possibly causing dehydration, which might raise the risk of damage to the appendix, BBC reports.
Dr Emmanual said it was also possible that the apparent link between appendicitis and air pollution - both common phenomena - could be spurious.