Two new scientific studies on how cellphone radiation affects the health of mice and rats have failed to resolve questions over whether cellphone use has a detrimental effect on human health.

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Academic journal Science explains that cellphones "emit non-ionizing, electromagnetic radiation" similar to that used by microwaves, "but scientists have struggled to conclusively link cellphone use to cancers or other illnesses."

For two years, rats and mice were placed for nine hours a day in "reverberation chambers" and exposed to radiation from 2G and 3G frequencies that either matched or exceeded those allowed by U.S. regulations.

John Bucher, co-director of the study, said that such exposure "is not a situation that most people will encounter when using cellphones... (but it allows) us to explore the potential for biological effects if they're going to occur."    

The test subjects showed a species- and sex-dependent increased risk of tumors in the connective tissues surrounding nerves in the heart; lymphoma; cancers of the prostate, skin, liver, lung and brain; lower birth weights; DNA damage and heart conditions.

However, scientists were unable to clearly determine whether the conditions were caused by radiation exposure.

According to Science, the findings "will not dramatically reshape the debate over cellphone safety... both critics and supporters of current risk evaluations and safety standards claim the studies support their points of view."

The studies were conducted by the National Toxicology Program at the request of the U.S. Food and Drug Administration (FDA) as part of a US$25 million research program.

The FDA, a key actor in cellphone regulation, concluded "the findings don't suggest that U.S. regulations on cellphone radiation need to be tightened."

The results of a major European study on cellphone use and the risk of brain tumor are due to be released later this year.