INTRODUCTION
Skin aging is a multifactorial process resulting from both intrinsic and external factors. Intrinsic functional alterations resulting from metabolic slowdown that cumulates with age is a major factor resulting in skin aging. External environmental factors include: exposures to solar rays, pollutants such as ozone, smog or particulate matter or lifestyle factors (smoking, alcohol consumption etc). A combination of all these factors leads to a premature skin aging leading to the perception (self-perceived or perceived by others) of an older look than the true chronological age of the skin The major extrinsic factor of skin aging is UV rays, as evidenced by the clearly altered condition of naturally uncovered skin areas such as the face and dorsum of hands. Extensive studies have demonstrated the damaging effects of acute and chronic solar UVB rays1 on epidermal cells including DNA damage, mainly on Caucasian skin. However, the last two decades have emphasized the insidious effects of the far more abundant and common (no zenithal hours) UVA rays that penetrate much deeper into skin and that, unlike UVB, are not associated with warning signs such as erythema/sunburn. UVA’s are indeed strong inducers of oxidative stress through generating reactive oxygen species (ROS) and of early signs of skin aging through dermal damage2 and pigmentation disorders. Facial wrinkles, mottled uneven pigmentation, pigmented spots, laxity, and sagging are usual UV-related photo-aging signs.1 Recently, specific signs of skin aging according to skin color have been identified.3 Other extrinsic factors are tobacco and pollutants, as high-lighted by recent studies. Tobacco smoking reduces elastin and collagen I-III synthesis resulting in older skin appearance and dull complexion.4 The skin of subjects who live in highly polluted cities presents higher oxidative stress, higher lactic acid content, and a lower hydration level, as compared to those living in less polluted areas.5-8 Developed or fast emerging societies express an overall growing concern for a younger look. Accordingly, there is a strong demand for rejuvenating cosmetic products, treatments, and techniques to reduce wrinkle appearance, restore skin texture, smoothness, radiance, even pigmentation, and to lighten aging spots, etc. This article focuses on cosmetic ingredients that aim at alleviating the signs of both chronological and environmen- tal skin aging, with proven/controlled results of efficacy.
1. Development of Novel Testing Methods
The first requirement for developing a skin anti-aging cosmetic ingredient lies in developing reliable instruments for objective measurements of changes occurring in aged condition and appearance of skin. Visual grading methods for affording quantitative support to clinical evaluation or self-appraisal of subjects are now available together with instrumental/objective methods of skin properties, or imaging the skin surface relief or the ultra-structure of skin at various depths as well as determining the location and amount of various biological molecules of interest, such as melanin, collagen, and elastin.9 Photographic charts for grading signs of aging in Caucasian, Asian, dark-skinned subjects have been published.3 Evaluation scores can be determined by trained individuals at baseline and different time-points of product application or follow up post treatment or sessions. The palette of techniques9 used for assessing age-related skin properties and effect of treatment, which include high-frequency ultrasound, laser confocal microscopy, optical coherence
