Free radicals are highly reactive molecules that can damage other molecules by ‘stealing’ electrons from their atoms. Reactive oxygen species or ROS are free radicals that are derived from oxygen, while oxidative stress is the term used to describe the damage sustained by cells due to the production of ROS. ROS are a natural byproduct of normal cellular function. Inflammation also generates ROS. Many environmental factors such as cigarette smoke, radiation, and high fat, high sugar diets can lead to increased oxidative stress.