No one seems to explain what exactly one is.
Free radicals are highly-reactive and unstable molecules that can cause serious cellular damage.
These molecules contain atoms with unpaired electrons. An unpaired electron has a tremendous pull on the atoms of other cells causing these cells to become disrupted, this can cause a chain reaction resulting in many aging problems. This aging is like oxidation of the body similar to metal rust. Free radicals are produced not only through normal bodily processes, but also from other sources such as air pollution and tobacco smoke. All of the cells in our body are continually exposed to these damaging molecules, which many scientists now believe may contribute to the development of a host of chronic diseases, including cancer, premature aging, cataracts, heart disease, senility and arthritis.