Ten or more years of mobile phone use increases the risk of developing acoustic neuroma, a benign tumor on the auditory nerve, according to a study released on Wednesday by Sweden’s Karolinska Institute.

The risk was confined to the side of the head where the phone was usually held and there were no indications of increased risk for those who have used their mobile for less than 10 years, the Karolinska Institute said in a statement.

The institute, one of Europe’s largest medical universities and a clinical and biomedical research center, awards the Nobel Prize in physiology or medicine.

“At the time when the study was conducted only analog mobile phones had been in use for more than 10 years and therefore we cannot determine if there results are confined to use of analog phones or if the results would be similar also after long-term use of digital (GSM) phones,” it said.

The mobile phone market is now dominated by GSM phones, which replaced the bulkier and less advanced analog phones in many markets the mid- and late-1990s.

The mobile phone industry has said there is no scientific evidence of negative health effects from use of mobile phones.

The Karolinska Institute said 150 people with acoustic neuroma and 600 healthy people participated in the study.

“The risk of acoustic neuroma was almost doubled for persons who started to use their mobile at least 10 years prior to diagnosis,” the institute said.

“When the side of the head on which the phone was usually held was taken into consideration, we found that the risk of acoustic neuroma was almost four times higher on the same side as the phone was held and virtually normal on the other side.”

Finland’s Nokia is the world’s biggest mobile phone maker.

Other large producers include Motorola of the United States, South Korea’s Samsung Electronics, Germany’s Siemens and Swedish-Japanese joint venture Sony Ericsson.

Global mobile phone sales have been booming as thousands of new users sign up every day and existing subscribers replace their old handsets with new ones, capable of taking pictures or playing music.