In Vivo Studies of the Evolution of Physical Properties of the Human Skin with Age

Abstract

In vivo measurements taken by valid methods, help to interpret the phenomena associated with the aging process. The authors developed some routine techniques to measure physical properties of the skin both deep in the dermis-epidermis and at the surface (stratum corneum). Measurements on the forearm of 150 people yielded the following results regarding the dermis-epidermis level: (1) skin thickness begins to decrease at 45 years of age for men and women, when women's skin becomes thinner than men's skin; (2) torsion extensibility, normalized for a given skin thickness, sharply decreases after 35 years of age; (3) skin optical properties are modified, ie the photoplethysmographic signal, measured on the forehead, greatly increase after 60 years of age; (4) at the cutaneous surface level, the main modifications are increased shedding of stratum corneum after 60 years of age in parallel with a modification of the stratum corneum cohesivity, altered skin microrelief during the aging process, and slightly decreased transepidermal water loss while the corneocyte projected size increases. These findings allow consideration of the aging process at the skin level as a phased process. The alterations of the physical properties and their kinetics suggest a various process according to the different cutaneous sections.

Skin Conductance at 24 Source (Yuan) Acupoints in 8637 Patients: Influence of Age, Gender and Time of Day

“…Also in agreement with psychophysiological research, we observed that SC at acupoints decreases with age in both genders [19,20]. This finding generally coincides with the first clear agerelated changes in the skin of adult humans that appear between the third and fourth decades of life, changes that may be accounted for by a relatively sudden decrease in skin thickness and elasticity occurring in the fourth decade [21]. In addition, we found significantly higher afternoon SC readings in both genders, consistent with increased sympathetic autonomic nervous system activity in the afternoon [22].…”

The aged epidermal permeability barrier. Structural, functional, and lipid biochemical abnormalities in humans and a senescent murine model.

“…C-E, osmium tetroxide; A, B, F, and G, ruthenium tetroxide. (14) alone can account for the decreased TEWL in aged epidermis. A combination of these factors could be operative.…”

“…A combination of these factors could be operative. In contrast, it has been long known that aged epidermis is abnormally permeable to a variety of drugs in in vitro systems (14)(15)(16). Thus, it seemed likely to us that the seemingly normal and even subnormal levels of TEWL displayed by intrinsically aged epidermis might mask an underlying lack of functional reserve.…”

“…Likewise, only minor functional abnormalities have been reported in aged epidermis. Stratum corneum water content is reportedly normal (8)(9)(10)(11) or slightly decreased (12), and only slight differences in barrier function have been reported both in vitro (1) and in vivo (9,13,14). Yet, drug permeability appears to be significantly altered; for example, the in vitro permeability of water-soluble dyes, such as fluorescein, is increased ( 15), while the permeability of lipidsoluble drugs, such as testosterone, is decreased (16).…”

Using optical coherence tomography to evaluate skin sun damage and precancer

“…Fitting to a line was considered appropriate because an exponential decrease in backscattered light intensity with depth occurred, yet the demodulation electronics performed a logarithmic function on the detected signal. Because previous studies have found differences in skin with age [12,13], the data were analyzed to determine whether sorting by age or sex was necessary. Images on both the forearm and upper inner arm were evaluated.…”