In the last century, dense, pigmented bodies were observed on nerve cell sections, and the quantity of those pigments in the neurons was correlated to the age of the individual. Light microscopy has shown the presence of the pigments in the cells of most tissues and organs in both vertebrates and invertebrates, and they have also been seen in cultured cells. However, these commonly found cellular components have only have studied in detail since the last 25 years, using electron microscopic, histochemical and biochemical techniques to try to describe their nature, origin, development and possible physiological role. The comparable morphology, composition and physicochemical properties of these various pigments indicate that they are all produced by the same biochemical mechanism, including: 1) the peroxidation of the polyunsaturated fatty acids of cellular membranes by free radicals; 2) the reaction of lipid peroxidation end-products(s) with proteins, giving fluorescent polymerized compounds; 3) the combination of those polymerized elements and the peroxidized lipids. Different names have been used for these pigments, the most common of which in English are: "age pigment", "ceroid" and "lipofuscins". However, due to their common origin and their fluorescence, they are tended to be grouped under the term lipofuscins (in French: lipofuscines). Recent studies have confirmed that cellular lipofuscin concentration is definitely related to the physiological age of the individual. This concentration varies depending on the tissue and the organ; it is controlled by intrinsic regulatory factors, but also by environmental conditions, such as nutrition, physical activity, stress and hygienic conditions.