Despite a recent move to classify mobile phones as possibly carcinogenic, the scientific evidence increasingly points away from a link between their use and brain tumors, according to a new study.
It also found a lack of established biological mechanisms by which radio signals from mobile phones might trigger tumors.
"Although there remains some uncertainty, the trend in the accumulating evidence is increasingly against the hypothesis that mobile phone use can cause brain tumors in adults," the experts wrote in the journal Environmental Health Perspectives.
The latest paper comes just two months after the World Health Organization's (WHO) International Agency for Research on Cancer (IARC) decided cell phone use should be classified as "possibly carcinogenic to humans."
Anthony Swerdlow of Britain's Institute of Cancer Research, who led the new review, told Reuters the two positions were not necessarily contradictory, since the IARC needed to put mobile phones into a pre-defined risk category.
"We are trying to say in plain English what we believe the relationship is. They (IARC) were trying to classify the risk according to a pre-set classification system," Swerdlow said.
Other things deemed by the IARC to be possibly carcinogenic include items as diverse as lead, pickled vegetables and coffee.
Mobile phone use has risen hugely since the early 1980s, with nearly 5 billion handsets in use today, and controversy about their potential link to the main types of brain tumor, glioma and meningioma, has never been far away.
The largest study to date, published last year, looked at almost 13,000 mobile phone users over 10 years.
Swerdlow and colleagues analyzed its results in detail but concluded it gave no clear answer and had several methodological problems, since it was based on interviews and asked subjects to recall phone use going back several years.
Significantly, other studies from several countries have shown no indication of increases in brain tumors up to 20 years after the introduction of mobile phones and 10 years after their use became widespread, they added.
Proving an absence of association is always far harder in science than finding one, and Swerdlow said it should become much clearer over the next few years whether or not there was any plausible link.
"This is a really difficult issue to research," said David Spiegelhalter, Winton Professor of the Public Understanding of Risk at the University of Cambridge, who was not involved in the study.
"But even given the limitations of the evidence, this report is clear that any risk appears to be so small that it is very hard to detect, even in the masses of people now using mobile phones."
Swerdlow is chairman of the International Commission on Non-Ionizing Radiation Protection's Standing Committee on Epidemiology. The commission is the international body, recognized by the WHO, that constructs guidelines for exposure limits for non-ionizing radiation.
Since mobile phones have become such a key part of daily life, used by many for web surfing as well as talking, industry experts say a health threat is unlikely to stop people using them.