During the past 25 years, the field of free radical biology has germin
ated, sprouted, and flowered. Free radicals derived frommolecul ar oxy
gen, formerly of interest only to radiation chemists, are now known to
play multiple roles in living systems. We will here consider the gene
ralities of this field with some special focus on skin as a site of ox
ygen radical production and as a target upon which the damaging propen
sities of these radicals are exerted.