The attachment of glucose to skin collagen triggers a series of spontaneous chemical reactions that culminate in the formation and eventual accumulation of irreversible cross-links between adjacent collagen molecules. The extensive cross-linking of collagen causes the loss of skin elasticity characteristic of aging. The steps by which glucose alters skin collagen have been understood by food chemists for decades and only recently have biologists recognized that the same steps take place in the skin. The glucose and amino group combine forming what is called a Schiff base. This combination is unstable and quickly rearranges itself into a stabler, but still reversible, substance known as an Amadori product.
AGEs are yellowish in color, and contribute to the yellowing of skin and age spots.
AGEs are highly reactive, and in a final series of reactions, cross-link an adjacent collagen molecule. The skin is always in contact with the air and oxygen, and increasingly exposed to ultraviolet radiation. As a result, the risk of photoaging induced by oxygen radicals has increased substantially. Besides those photosensitizers that are naturally in skin, skin is also increasingly exposed to photosensitizers found in air pollution, cosmetics, plant extracts, and medications. Recent research has revealed that UVA photogenerated singlet oxygen radicals cause skin damage by disrupting the natural balance found in the skin by stimulating the synthesis of collagenase, which is an enzyme that degrade collagen, without countering it with the synthesis of anti-collagenase that holds skin degradation in check.