text: can cell phone usage cause damage to your ears or brain?   provided by david schoppik, hhmi predoctoral fellow, university of california, san francisco  the question is something to think about, given that cell phones seem to be everywhere. first, i'll describe a scenario in which cell phones might be expected to cause some damage, using skin cancer as an example, and then i'll review some of the scientific work that has tried to examine this scenario.  the short answer is, as far as we know, no, cell phone usage can't cause damage to your ears or brain. it has been known for a long time that certain environmental conditions are associated with higher rates of cancer, though. these conditions have led to changes in behavior, since we would all like to avoid cancer.  take exposure to sunlight. a bronze tan used to be associated with health and vigor. now it is thought to be healthiest to put on sunscreen because overexposure to the sun's rays is linked to various skin cancers. how does that cancer happen? the sun's rays are a form of energy, which can have different effects on skin. immediately (and pleasantly), that energy is noticed in the form of heat as our skin warms up. a bit more exposure and the skin changes its pigment (that is, it tans), which changes the amount of sunlight absorbed.  but repeated, long-term exposure has been shown to be damaging. it turns out that the increased energy, every once in a while, can actually break or change the bonds of some of the molecules that make a skin cell work. most of the time, these breaks are harmless—the cell just dies, the break is repaired, or it makes no difference because the place where the break occurred isn't all that important.  sometimes, though, the change brought about by the increased energy (coming from the sunlight) is the sort of break that changes the way something in the cell functions—a real mutation. all skin cells normally go through a cycle where they wait for a while, then replicate, and then die. the signal to die is a carefully regulated process that's an important way to make sure we don't end up with old, sick cells (cell death of this kind is usually called apoptosis). if there is a cell with a mutation in the part of the cell's blueprint (the dna) for the pathway that controls the signals to die, you end up with a cell that may just think it should go on living forever.  at first glance, that doesn't sound so bad. but what if this same cell also decided to keep on replicating? each cell that replicated would also live forever and keep replicating forever. you'd end up with a fast-growing immortal bunch of cells, more commonly known as a tumor.  but what do tumors have to do with cell phones? well, it turns out that cell phones are quite similar to the sun in that they also emit energy—that's how they can send our conversations over long distances. and while the sun is much stronger, it's also much farther away. so if we hypothesize that the energy from cell phones will be harmful, one thing we can look for is the presence of tumors—either skin tumors on the ears or brain tumors. we can also expose animals to the type of energy that cell phones emit and see if they do worse than animals that haven't had that exposure.  let's see what scientists have found:  study 1: in 2003, a group of british scientists exposed bacteria (special ones that were similar to human brain cells) to energy similar to that emitted by cell phones and found no difference between them and unexposed bacteria. this is a pretty good direct test of our hypothesis.  study 2: in 2004, a group in italy looked at the sorts of damage that usually occur when cells are exposed to large amounts of energy. they found that cells exposed to cell-phone-like energy did not show more damage than cells that weren't exposed.  study 3: a group in sweden showed in 2004 that there was no link between cellular or cordless telephones and tumors in the mouth in human