ABSTRACT
This chapter overviews the essential structural elements of the skin and their key functions relevant to skin absorption pathways and sensations and somatosensory systems. Normal skin consists of three main layers: epidermis, dermis, and hypodermis. Skin appendages include nails, hair, sebaceous glands, eccrine glands, and apocrine glands. Measuring the physical characteristics of the skin using biophysical instruments provides key information about various skin parameters. Measurement of skin surface pH is used to assess the acidity of the surface of the skin, which can vary according to the time of the day, the skin site, and between individuals. Desquamation is used to assess the structure and biological dynamics of stratum corneum (SC) and to investigate the effect of drugs and topical products on the skin. Transepidermal water loss (TEWL) varies in different anatomic sites and is inversely related to the corneocyte size. Skin microcirculation and perfusion can be affected by a number of exogenous and endogenous factors.
