They're highly reactive and they can cause damage to the cells of our body. So Ros stands for reactive oxygen species. Now, of course, the electron transport chain isn't a perfect process and these molecules will, in fact, form. And that's exactly why, as we'll see in just a moment, we have enzymes that can actually control the formation of these harmful byproducts. So generally speaking, if these reactive oxygen species produce are not actually controlled, ros can actually react with cell components and cause something called oxidative damage. In fact, it's oxidative damage that is linked to the process of aging.