[The biological basis of aging. The free radicals theory]

Several theories were formulated to explain the process of aging. Now they often appeared out of date. The free radical theory is a rather recent one that is based on the production of free radicals during normal physiological respiration. A lot of data indicate their role in the progress of aging. Clearly also other factors play a role in this process: the toxicity of free radicals may for instance depend on the availability of free iron. So on the one hand we need oxygen for existence and free radicals may destroy infectious bacteria; on the other hand oxygen appears to be toxic and may be supposed to underly the process of aging.