Some chemicals might have a harmful effect on our health and safety depending on our level of exposure to them. Scientists generally assume that such effects are proportional to the amount or “dose:” The more you are exposed to them, the more likely the possibility of an effect. However, some studies have identified effects at very low doses but not necessarily at higher doses. But there is much scientific uncertainty of such low-dose effects and the weight of evidence given to low-dose studies is generally low. A European Food Safety Authority toxicologist highlights the key concepts underlining the “low-dose hypothesis” and what dose-response typically means to human health.