Human skin is continuously exposed to free radicals; not just ultraviolet (UV) solar radiation but the visible and infrared range of the spectra, as well. Sun exposure leads to the production of free radicals in the skin. These highly reactive molecules serve an important function in humans, acting against viruses and bacteria as well as processing signals on a cellular level. However, if the concentration of free radicals exceeds a critical level, cells and their compartments can be harmed. UV radiation is, in fact, a major cause for sunburn, photodamage, premature skin aging and skin cancer. Sun exposure also leads to damage in skin’s elastic fibers, i.e., elastin and collagen, resulting in premature aging.
The body’s own antioxidant systems can provide a complex defense against free radicals, counteracting their highly reactive and destructive effects and neutralizing them to prevent cell and tissue damage. Antioxidants in human skin include carotenoids and vitamins, as well as various enzymes. Since humans cannot produce these substances naturally, they must be supplemented in the diet, particularly in the form of fruits and vegetables. In fact, research has shown that individuals consuming high levels of fruits and vegetables rich in carotenoids have lower incidences of skin pathology. In vitro and in vivo evidence demonstrates the role of endogenous carotenoids in the systemic protection and maintenance of skin health. In this article, they are considered for potential photoprotection.
Chemistry of Dietary Carotenoids
Carotenoids are yellow, orange and red pigments synthesized by plants. Those most common in North American diets are α-carotene, β-carotene, β-cryptoxanthin, lutein, zeaxanthin and lycopene. Most carotenoids have a polyisoprenoid structure with a long chain of conjugated double bonds and nearly bilateral symmetry around the central double bond. Carotenoids are tetraterpenoid compounds containing 40 carbon atoms arranged in a repeating pattern of five carbon units.