Challenge and promise

We are witnessing an unprecedented and rapid expansion in the elderly populations of the developed and developing worlds. The effects of age-related frailty, disability, and disease combine to present an immense and growing cost to society in terms of health and social service expenditure, impaired quality of life, and physical and emotional suffering. Research that can lead to novel interventions that extend life spans and improve quality of life for the elderly has the potential to exert enormous impact on this ever-aging society. Our skin displays the first signs of aging. Considering the fact that a collection of human internal organ specimens for experimental research purposes faces major practical and ethical obstacles, the skin may be viewed as a promising tool for aging research. With age, skin undergoes major morphological and physiological changes and, consequently, becomes fragile and prone to various diseases. Understanding the mechanisms behind skin aging is the first step toward prevention of these various diseases. This special issue on skin aging is supported by renowned aging researchers and is aimed at dermatologists and other scientists working in the fields of biology, biogerontology, bioinformatics, and gender-medicine. Another potential audience includes politicians interested in state-of-the-art research on this topic. The issue is divided into three parts. In the first part, the reader receives an overview of current knowledge about the pathomechanisms of aging skin. Andrea Vierkötter and Jean Krutmann summarize the influence of several environmental factors on the initiation of skin aging. Among them, sun exposure, air pollution and smoking present ethnic-specific manifestations of extrinsic aging. Nicolai Treiber et al. focus on the oxidative stress theory, presenting the important role of the antioxidant balance in the aging process and showing recent research data about the mitochondrial superoxide dismutase 2. In the review of Florence Debacq-Chainiaux et al., the terms replicative senescence and stress-induced premature senescence (SIPS) are described in detail, and the reader has the opportunity to learn more about in vitro models that have been developed for studying the long-term effects of UV and stress on several skin cell types. There is no doubt that hormones play a key role in the regulation of skin homeostasis and in the aging process. Jörg Reichrath describes Challenge and promise Human skin aging