[Skin aging].

For decades it has been appreciated that aging is the consequence of both genetic and environmental influences. Genetic factors are evident, e.g., in the >100-fold variation among species in the rate of aging; and recent studies of fruit flies, worms, and even mice have identified specific longevity genes whose modification can greatly alter lifespan [22]. Conversely, a role for environmental factors can be deduced both from epidemiologic and laboratory-based experimental data. Such influences include ionizing radiation, severe physical and psychological stress, overeating versus caloric restriction, and in the case of skin ultraviolet irradiation. In this regard, skin is no exception as skin aging results from intrinsic (genetic, endocrinologic) and extrinsic (environmental) factors. In this chapter I will focus on extrinsic skin aging for the following reasons: (a) The overall topic of this chapter is functional food for skin or, in other words, manipulation of skin aging by nutrition-based strategies; (b) It has already been shown for topical approaches (sunscreens, cosmeceuticals, etc.) that extrinsic skin aging can be effectively manipulated. (iii) And thus, nutrition-based anti-skinaging strategies will be most effective if they are directed against extrinsic skin aging. Extrinsic and intrinsic skin aging can be clearly distinguished at a clinical, histological, and molecular level. The two most prominent clinical signs of extrinsic skin aging are the formation of coarse wrinkles and an increase in the number of pigment spots (Fig. 2.1). Interestingly, ethnic differences exist, because, e.g., Caucasian women develop earlier and more severe skin wrinkling whereas Japanese women show more lentigines at a younger age. Among all environmental factors, solar ultraviolet (UV) radiation is most important for extrinsic skin aging, a process accordingly also termed photoaging. Within recent years substantial progress has been made in elucidating the underlying molecular mechanisms. From these studies it is now clear that both UVB (290–320 nm) and UVA (320–400 nm) radiation contribute to photoaging. UV-induced alterations at the level of the dermis are best studied and appear to Skin Aging