 Imagine you take a lung full of air laced with toxic chemicals. How do you know what the risk is of something unpleasant happening to you? Risk bites has already covered the difference between hazard, the potential of something to cause harm, and risk, the probability or chance of harm occurring. What we need to know is how do you get from one to the other? If you want to put a number on the risk of something bad happening, dose response is what you need. But what is it exactly? Try this experiment. Hold your right ear lobe very lightly between your right index finger and thumb. What do you feel? Probably not a lot. Now increase your hold slightly. You probably feel an increase of pressure on your ear. Now pinch hard. Do you feel the pain? Congratulations, you have just experienced dose response. The dose is the amount of pressure you put on your ear lobe and the response is the pain you feel. The greater the pressure, the greater the response. Dose response is simply the relationship between how much of something our body is exposed to and the way it responds to that something. When it comes to chemicals, the dose is the amount of stuff that gets to a particular part of the body where it can do harm. And the response is the harm a given amount of stuff does. This becomes pretty important when a small amount of something is safe or even good for you while a large amount might kill you. A German Swiss dude called Paracelsus put his finger on it metaphorically speaking in the 16th century when he declared that it's the dose that makes the poison. And in saying so he became the father of modern toxicology. Dose response is what allows scientists to connect hazard to risk and to put a number on the probability of something bad happening and because of this it is incredibly powerful. But as we'll see in future risk bites in this series, it can also get rather complex. We'll be looking more closely at dose response and how it helped shed light on risk over the next few months. But until then, stay safe.