Source:http://linkedlifedata.com/resource/umls/id/C1517312
NCI: Free Radical Formation involves production in normal or pathological processes of chemically unstable, short half-life and highly reactive molecules carrying at least one unpaired or 'free' electron in the outermost electron shell. Appropriating electron(s) from a nearby molecule and damaging that molecule by altering the electron number in its outermost electron shell, Free Radicals produce tissue damage.