Researchers in Australia have reported one of the first scientific hypotheses that normal mobile phone use can lead to cancer. The research group, lead by radiation expert Dr Peter French, principal scientific officer at the Centre for Immunology Research at St Vincent's Hospital in Sydney, said that mobile phone frequencies well below current safety levels could stress cells in a way that has been shown to increased susceptibility to cancer. The paper, published in the June issue of the science journal Differentiation, says that repeated exposure to mobile phone radiation acts as a repetitive stress, leading to continuous manufacture of heat shock proteins within cells. Heat shock proteins are always present in cells at a low level, but are manufactured in larger amounts when the cell is stressed by heat or other environmental factors. They repair other proteins that are adversely affected by the conditions, and are part of the cell's normal reaction to stress. However, if they are produced too often or for too long, they are known to initiate cancer and increase resistance to anti-cancer drugs. Dr French emphasised that no link has yet been shown between the specific biological effects of mobile phone radiation and cancer, but that there was now a theoretical framework for such an effect that could be investigated. His previous work has included showing that the production of histamine, a chemical involved in asthma, can be nearly doubled after exposure to cellular frequencies. To date, most safety levels have been set on the assumption that damage is caused by heating effects of radio waves in human tissue, much higher than the levels at which Dr French claims heat shock proteins are triggered. His co-authors include Professor Ron Penny, the director of the Centre and one of Australia's leading experts in the cellular effects of HIV, and Professor David McKenzie, head of applied physics at Sydney University. How can you get access to information and entertainment from just about anywhere? Find out the latest in ZDNet UK's Mobile Technology News Section. Have your say instantly, and see what others have said. Click on the TalkBack button and go to the ZDNet news forum. Let the editors know what you think in the Mailroom. And read other letters.