 How would you estimate health risk from chemicals and other substances? Last week's RiskBytes talked about health risk as the probability of something bad happening to your health. It's the kind of thing you might want to know if you want to increase your chances of avoiding getting sick or injured, but how do you go about putting a number on health risk? It's not easy, especially as we're trying to predict the future here, and there are many things that can influence how something might affect your health. But over the years, scientists have developed a way of taking at least some of the guess work out of assessing risk. Imagine for instance, you're handling some mystery substance, let's call it unobtainium. How would you go about working out what the risk is? The first step is to consider the potential for this unobtainium to cause harm if it got into your body, and what harm it might cause once it gets there. This is the hazard it presents. It gives an idea of how nasty the stuff is if you come into contact with it. But hazard alone doesn't say anything about risk. It doesn't matter how hazardous the unobtainium is, if you're not exposed to it, it cannot directly harm you. So the next thing we need to know is how much unobtainium you're exposed to, including how it gets into your body and where it goes once it gets there. We're getting close to being able to estimate risk at this point, but there's still something missing. We need to know how much unobtainium causes what sort of effect. If we can measure this or estimate it, we can connect hazard and exposure to the probability of harm occurring, risk in other words. This is the dose-response relationship, and this is what transforms hazard and exposure into a measure of risk. Of course we still need to know what to do with this measure of risk, but that is a story for another day. For more insights into the science of risk, don't forget to subscribe to Risk Bites.