Oxidative stress is the result of an imbalance between the production of oxygen free radicals and the ability to detoxify them, or repair the resulting damage they cause. Reactive oxygen species (ROS) form as a byproduct of the metabolism of oxygen and include oxygen ions, free radicals, and peroxides. Environmental stress can cause ROS levels to increase dramatically. This can result in significant cellular damage cumulating in an effect called oxidative stress. Oxidative stress has been linked to aging, neurodegeneration, cancer, and other diseases in humans.