As mobile phones began to increase in popularity, concerns arose that long-term cell phone could cause brain tumors. But a major, decade-long international study which researchers hoped would settle the issue has instead proved inconclusive.

According to The Associated Press, a 10-year survey of almost 13,000 participants found most cell phone use did not increase users’ risk of developing meningioma, a common and frequently benign tumor, or glioma, a rarer but deadlier form of cancer.

The study, conducted by the World Health Organization’s International Agency for Research on Cancer, found that there were “suggestions” that using cell phones for more than 30 minutes each day could increase the risk of glioma, the AP reported. But the authors added that “biases and error prevent a causal interpretation” that would directly blame cell phone radiation for the tumor.

Cell phones carry radio waves that are similar to those of microwave ovens, but there is no support for the claim that these waves have negative effects on the body.

Researchers also admitted that cell phone use has greatly increased in the decade since the study began, possibly skewing the numbers.

“The users in the study were light users compared to today,” Professor Elisabeth Cardis of the World Health Organization’s International Agency for Research on Cancer told

Critics of the study also argue that its creators ignored several important factors, including the slow growth rate of brain tumors, which could take up to 25 years to form.

Creators of the study plan to release a comprehensive overview of available research within two years. Researchers are also looking to see if cell phones increase the development of cancerous tumors in the ear’s acoustic nerve. Another study will also examine cell phone’s affects on children, who many believe are more susceptible to radiation.

“Until stronger conclusions can be drawn one way or another it may be reasonable to reduce one’s exposure,” Cardis told “One way to do this would be to make calls using a hands-free device.”