I am a retired lecturer in Biology from Imperial College London.

There is no doubt that prolonged exposure to mobile phone radiation does cause DNA damage in some cell lines. We cannot expect all cell lines to behave in the same way because of natural biological variability. We are all the products of thousands of genes that interact in countless ways so that each one of us is both physically and biochemically unique. We do not all get the same side effects from taking a medicinal drug and we cannot therefore expect to respond in the same way to electromagnetic insults.

Also, it is not a valid argument to say that because we do not understand the mechanism by which the DNA damage occurs, then it cannot happen. However, if you want a plausible mechanism visit http://tinyurl.com/5ru6e6 . In essence it says that the loss of structurally important calcium ions weakens cell membranes and makes them more inclined to develop temporary pores and leak. When this happens to lysosome membranes, they leak digestive enzymes that then damage the cell's DNA.

Having said that, most of the severely damaged cells will die naturally, but others may remain as clones of aberrant but benign cells that increase in number with increasing exposure to the radiation. However, we would expect some to be genetically unstable and mutate, with natural selection favoring the more rapidly growing and aggressive ones until we get a full-blown cancer. But even then, the immune system should be able to nip it in the bud; that is until the immune system fails due to old age or is compromised in some way. Consequently, the likelihood of developing mobile phone-related cancer will depend on genotype, duration of exposure and the state of the immune system.

However, the reported effects of living within a few hundred metres of a base station cannot be explained so easily. The low signal strength at this distance demands an exquisitely sensitive mechanism to detect the radiation. Unfortunately (for us) there is such a mechanism. It lies in the magnetically sensitive pigment cryptochrome. The cryptochromes are a family of pigments present in virtually all animals, plants and some bacteria. They are used to sense the presence of light, or the direction of the Earth's magnetic field in animals that use it for navigation. They also form an integral part of the biological clock that controls their circadian rhythms.

Put very simply, cryptochromes can measure magnetic fields because they absorb light and use its energy to drive an electron between two parts of the molecule to form a pair of magnetic free radicals. The electron then finds its way back, but the process is delayed by any external magnetic field, so that the amount of pigment in the free radical form at any one time is a measure of the field. Much of the cryptochrome is in the eye, where its different orientations in the curve of the retina probably enables migratory animals to "see" the field possibly, as an extra colour superimposed on their fields of vision.

Ritz et al. demonstrated this very clearly, when they showed that robins were able to orient in the geomagnetic field when given light of the wavelengths absorbed by cryptochrome. However, even more significantly, they found that oscillating electromagnetic fields within the range 0.1-10MHz at 0.085 microtesla (about 500 times weaker than the Earth's steady field) completely disrupted the system and the birds were unable to orient. (Ritz et al. Nature. Vol. 249 13th May 2004). It may be significant that this range of frequencies includes the bit-rates (rates of transmission of individual digital pulses) of many forms of digital wireless communications, including mobile phones, DECT cordless phones and Wifi. It seems likely that these forms of low level radiation may also interfere with the birds' ability to navigate.

We humans have no natural ability to navigate using the Earth's magnetic field, and we sense light to synchronise our circadian rhythms using melanopsin. But we still have cryptochromes, much of it concentrated in the pineal gland, where, in conjunction with the suprachiasmatic nucleus, it appears to regulate the biological clock that leads to the rhythmic production of melatonin. Much of the work on the biological clock has been done on mutants of the fruit fly Drosophila, and this too appears to be affected by magnetic fields (see Yoshii et al. 2009 http://tinyurl.com/cx7xaa ). They did not test oscillating fields, but a 300microtesla steady field could alter the rhythm of the clock or even stop it altogether.

The main significance of the biological clock for humans is that it controls our natural circadian rhythms, which enable us to anticipate the coming of dawn and dusk and diverts our body's resources to meet the demands of the new conditions. Many aspects of metabolism are controlled in this way; for example, during the day they are diverted to physical activity, but at night they are diverted more to the immune system and repair. If the rhythm were to fail or become weakened in amplitude, no process controlled by the clock would ever be able to function with maximum power. In particular, the immune system may never be able to summon the overwhelming power that is sometimes needed to overcome infection or cancer cells before they get out of control.

There is considerable anecdotal evidence for a weakened circadian rhythm in people living close to mobile phone masts, which include tiredness and loss of concentration during the day and poor sleep at night. The disruption of melatonin production during prolonged exposure to power line fields has been reviewed by Henshaw and Reiter (Bioelectromagnetics Supplement 7S86-S97 (2005)) and they argue that the effect on the rhythm may be similar to light.

The notion that weak electromagnetic fields have an effect similar to light is disturbing to say the least. In a paper reviewing the disruption of circadian rhythms in shift workers and others exposed to nighttime illumination Navara and Nelson. (J Pineal Research 2007 (http://tinyurl.com/afgLjr)) report an increased risk of breast and other cancers and a whole range of other health effects including insulin resistance, coronary heart disease, hypertension and myocardial infarction.

This clearly needs further investigation, but on present evidence, people living, and in particular sleeping, near a mobile phone base station may be at far greater risk of developing cancer than someone who just makes the occasional brief mobile phone call.

(for full context see http://scienceblog.cancerresearchuk.org/2008/07/25/do-mobile-phones-cause-cancer/)