WASHINGTON--Playing doctor on the Web often leads people to mistakenly believe that they are suffering from rare illnesses, according to a study by researchers at Microsoft.

"Web search engines have the potential to escalate medical concerns," or "cyberchondria," Ryen White and Eric Horvitz wrote in the study published by the Redmond, Washington-based software company on Monday.

They described cyberchondria as "unfounded increases in health anxiety based on the review of web content."

White, an expert in text mining, web search and navigation, and Horvitz, another Microsoft researcher who is president of the Association for the Advancement of Artificial Intelligence, noted that the Internet provides an "abundant source" of medical information.

"However, the Web has the potential to increase the anxieties of people who have little or no medical training, especially when web search is employed as a diagnostic procedure," they said.

"Common, likely innocuous symptoms can escalate into the review of content on serious, rare conditions that are linked to the common symptoms," they said.

For example, web surfers with a headache may determine they have a brain tumor or those with chest pain that they are suffering a heart attack.

"A brain tumor is a concerning possibility when a searcher experiences headache," the researchers said. "However, the probability of a brain tumor given a general complaint of headache is typically quite low."

"Such escalations from common symptoms to serious concerns may lead to unnecessary anxiety, investment of time, and expensive engagements with healthcare professionals," White and Horvitz said.

The researchers said the study was aimed at "improving the search and navigation experience for people turning to the Web to interpret common symptoms" and determining "the challenges that cyberchondria presents for search engine designers."

Microsoft's Live Search engine provided the Web search results for the study and MSN Health and Fitness provided medical search results.

The researchers also surveyed the health-related search experiences of 515 individuals.

According to other studies cited by the researchers, eight in 10 American adults have searched for healthcare information online.