Age and skin structure and function, a quantitative approach (I): blood flow, pH, thickness, and ultrasound echogenicity

Background/purpose: The aging process has been studied with fervor recently, given our shifting demographics. Since age's effects are so manifest in skin's appearance, structure, mechanics, and barrier function, it is not surprising that much effort has been placed in research to better understand them. Quantitative measurements permitted by bioengineering have allowed us to objectively and precisely study aging skin. These overviews piece together the immense amounts of information that have emerged from recent technological advances in dermatological research in order to develop a unified understanding of the quantitative effects of age on the skin. Methods: We performed a literature on age-related changes in blood flow, pH, skin thickness, and ultrasound imaging data, searching Pub-med, Em-Base, Science Citation Index, and the UCSF dermatological library's collection of books on the topic of aging skin. Results: Despite the many tools and techniques available for quantitative analysis of skin, age studies are often conflicting, especially in the areas of blood flow and skin thickness. Trends indicate that blood flow may decrease with age, especially in sites exposed to the environment. pH apparently varies little until the age of 70, after which it declines. Skin thickness data are difficult to interpret; while the stratum corneum is generally accepted to maintain its thickness during aging, dermal, epidermal, and whole skin thickness changes are controversial. Ultrasound reveals the appearance of a subepidermal low echogenic band that thickens with age, especially in environmentally exposed areas. Some studies also indicate the presence of an echogenic band in the lower dermis which thins with increased age. However, the whole dermis appears to become more echogenic in elderly people. Conclusion: Much remains to be done if we are to reach consensus on the effects of age on skin structure and function. Future studies would be benefited by increased standardization of skin sites tested, methodology, and increased sample size.