 In 2011, a study from the London School of Hygiene and Tropical Medicine revealed that one in six mobile phones in Britain is contaminated with fecal matter. In other words, they had poop on them. What was especially concerning was the presence of E. coli bacteria, a poop-related organism that you really don't want to be eating. Assuming that my fellow Britons don't have a particularly unusual bathroom habit in the grand scheme of things, you have to wonder why we don't see an epidemic of cell phone poop-related illness sweep the modern world. Of course, harmful bacteria are an unusual case as they're living organisms, but widespread exposure to dubious substances goes beyond the biological. For instance, numerous studies have shown that many of the banknotes in circulation around the world contain traces of cocaine, which when you've got your head around the disturbing mental image of poop on your cell phone begs the question, why aren't we all going around as high as a kite? The answer is that it's not just what we can measure that's important, but how much we're exposed to. Just because we can measure fecal bacteria on phones or restricted substances on banknotes doesn't mean that enough of the stuff is going to get into our bodies to have an effect. So when you come into contact with something that might be harmful, how do you know how much is too much? For that we need to know more about what happens when different amounts of the stuff get into the body. That gets us into dose response, and that is a topic for another risk bites. But in the meantime, it's safe to assume that there's an important difference between being able to detect something and that something presenting a significant risk. That said, you might want to think a little more carefully about your bathroom's cell phone habits in future just in case. For more insights into the science of risk, don't forget to subscribe to Risk Bites.