Age-related changes in the mechanical properties of human skin.

The mechanical properties of skin have been studied both in vivo and in vitro by a variety of test methods. These properties are well matched to the function of the skin, and they depend on the geometry of the collagen and elastin networks of the dermis. The time dependence of these properties is thought to be related to the "ground substance" components of the dermis. Age-related changes in the mechanical properties are a function of the degradation of the elastin network and of some as yet undefined changes in the viscoelastic properties of the "ground substance."     

Age-related changes in human dermal elastic fibres

Age-related changes in the human dermal elastic fibres were studied by scanning (SEM) and transmission (TEM) electron microscopy. The SEM findings showed an increase in the complexity of shape and arrangement of the fibres including flattening and branching, an increase in the roughness of the surface, and a decrease in interfibrillar areas. The TEM findings showed a decrease in microfibrils and amorphous material, and an increase in electron dense inclusions followed by the appearance of vesicular structure.     

Age-related changes in skin topography and microcirculation

Skin topography and microvasculature undergo characteristic changes with age. Although several non-invasive bioengineering methods are currently available to measure them quantitatively, few publications have referred to their relationship with age in different anatomical sites. This study was carried out to observe the age-related changes of the skin topography and skin microcirculation. The microrelief was assessed with special processing software from scanning by interference fringe profilometry of silicone replicas performed on two sites (volar forearm and back of hand) on 50 female volunteers (aged 20–74 years who consisted of ten probands in each decade). The superficial vascular network of both sites was assessed by videocapillaroscopy, and the subpapillary vascular plexus was studied with laser Doppler flowmetry. Skin color, which is affected by blood flow, was observed by colorimeter. The skin roughness and the mean height between peak and valley increased with age. There were statistically significant differences between the evaluated sites. This study also shows that the capillary loops in the dermal papillae decrease but the subpapillary plexus increase with age. The interference fringe profilometry associated with videocapillaroscopy may be useful and accurate to measure the efficacy of medical or cosmetic products to delay skin aging.     

Age-related mechanical properties of human skin: an in vivo study

We have investigated in vivo how various viscoelastic parameters that describe the mechanical properties of the human skin may vary with age. Accordingly, we have used a mechanical device that records the torsional extensibility of the skin. When submitted to a low torque, the time-response curve of the skin affords the determination of the immediate extensibility (UE), the immediate recovery (UR), the viscoelastic part of the deformation (UV), the elastic recovery (UR/UE), and the creep relaxation time (tau). Because the skin thickness varies with age and primarily governs the mechanical properties, it was measured through an ultrasound technique at the same sites (forearm) where the torque was applied. The results show that the skin maintains its thickness and extensibility up to the seventh decade as opposed to its elasticity or recovery capacities, which decrease from an early age. The viscous part of the deformation is constant through life, whereas the creep relaxation time decreases linearily with age. Except for skin thickness, no differences in these parameters between men and women were detected. The significance of these results are discussed in terms of structure alterations. The determination of the elastic recovery (UR/UE) appears to be a parameter of choice for illustrating skin aging.     

Age-related mitochondrial lipoperoxidation in human skin.

Mitochondria were isolated from the epidermis of human subjects of different ages by a procedure that included pretreatment of the tissue with bacterial protease before homogenization. That epidermal mitochondria catalyze enzymatic lipid peroxidation in the presence of NADPH and chelated iron (ADP-Fe3+) is indicated by the production of malonaldehyde. The process does not appear to be influenced by age, and it is strongly enhanced in preparations containing a small amount of melanin.     

Variations in facial skin thickness and echogenicity with site and age.

The characteristic pattern of reflectivity of facial skin, as evaluated by ultrasound, has not previously been described quantitatively. The aim of this study was to evaluate site- and age-dependent variations in skin thickness and echogenicity of facial skin. A total of 40 women, in different age groups, were studied at 12 different facial skin sites. Echographic images were recorded with a 20 MHz B-Scanner and processed by dedicated software. Skin thickness measurements showed significantly higher values on the lower part of the face, whereas skin echogenicity was higher on the upper part of the face. In elderly subjects, an increase in facial skin thickness and overall echogenicity was observed compared with the younger subjects at all assessed skin areas, except the infraorbital regions. Moreover, modifications of skin echogenicity according to age, consisting in the appearance of a subepidermal band and an enhancement of the lower dermis' reflectivity, were observable at most facial skin sites.     

Loss of elastic fibers causes skin wrinkles in sun-damaged human skin

BACKGROUND: Although wrinkling is the most obvious sign of aged skin, the detailed pathomechanism of wrinkle development has not been elucidated. OBJECTIVES: In this study, we investigated the role of elastic fibers in the formation of skin wrinkles. METHODS: Loss of elastic fibers was measured quantitatively in the facial skins of subjects representing seven decades, and then compared with wrinkle severities. We also investigated whether topical retinoic acid treatment to photoaged human skin can restore destroyed elastic fiber, and the correlation between wrinkle improvement with increase in elastic fibers in RA-treated facial skin. RESULTS: We found a significant correlation between decreases in the length, width, number and total area of oxytalan fibers and wrinkle severity. Furthermore, we found that topical application of retinoic acid (0.025%) to chronically photodamaged skin regenerated and restored elastic fibers, and that there was a significant positive correlation between the amount of newly regenerated elastic fiber and the wrinkle improvement caused by retinoic acid. CONCLUSIONS: Our results provide an objective insight into the role of elastic fibers in skin wrinkle formation by providing a quantitative correlation between changes in oxytalan fibers and the severity of skin wrinkling.     

Age-related changes in the resident bacterial flora of the human face.

Quantitative levels of resident aerobic and anaerobic bacteria of the face, show a characteristic age-related pattern. The density of anaerobic diptheroids and surface aerobic micrococci is higher in infancy than in early childhood. At puberty the quantity of organisms increases, with significantly higher levels achieved in late adolescence. Maximum counts are attained in early adulthood and remain constant until old age when a trend toward lower numbers occurs. These changes seem to correlate with the production of sebum.     

Evaluation of unique elastic aggregates (elastic globes) in normal facial skin by multiphoton laser scanning tomography

Background

There is no reliable marker to estimate the degree of skin aging in vivo. It now has become possible to quantitatively determine the dermal characteristics of the extracellular matrix (ECM) in vivo using multiphoton laser tomography (MLT).

Methods

Fifty-seven healthy Japanese female volunteers, aged from 20 to 60 years old, were examined using multiphoton depth-resolved measurements of autofluorescence (AF) and second harmonic generation (SHG) at three sites on their right cheek. Paraffin-embedded skin specimens obtained from the faces of 12 normal individuals aged 38-68 years old were stained with Elastica van Gieson (EVG).

Results

We found unique elastic aggregates at a 20µm depth from the dermo-epidermal junction (DEJ) in vivo which increased in size with aging of subjects from 20 to 60 years old. SHG fibers seemed to surround those elastic aggregates. Histological examination of specimens from normal individuals stained with EVG confirmed the occurrence of elastic aggregates with varied sizes just beneath the epidermis or hair follicles.

Conclusions

The elastic aggregates are morphologically similar to previously described ‘elastic globes’ and can serve as a marker of the early stage of photoaging. MLT will contribute to determine age-related dermal changes using a non-invasive technique.

     

Age-related changes in skin wrinkles assessed by a novel three-dimensional morphometric analysis

BACKGROUND: A system has been developed whereby the morphology of the skin surface can be evaluated directly in three dimensions. This system employs a non-invasive device that utilizes white light of halogen origin, and which allows the computation of wrinkle depth and width, and other parameters of skin surface morphology. Using innovative engineering, an optical system has been devised so that light is transmitted via a slit and can be used to measure not only replicas of the skin but also the skin surface directly. The measurement area is 6.4 x 6.4 mm, and the theoretical resolution with a x 50 magnification lens is within 12.5 micro m. OBJECTIVES: To use this system to study age-related changes in the morphology of wrinkles at the eye corner areas of women of varying ages. METHODS: One hundred and one healthy women (age range 20-80 years) residing in the Tokyo area were the subjects used in this study. RESULTS: Wrinkles demonstrated a rapid increase in depth in women aged 40 years or older, and plateaued at the age of 60 years. Surface morphology parameters yielded results similar to those of age-related changes in wrinkles. CONCLUSIONS: This new analytical system provides a rapid and convenient non-invasive method to evaluate skin surface morphology in three dimensions, especially with respect to wrinkle formation. The results obtained using this system provide a deeper insight into the mechanistic relationship between wrinkles and skin elasticity.     

日光对皮肤弹性的影响

目的观察日光和年龄对皮肤弹性的影响。方法问卷调查受试者（郊县组94例，市区组105例）的日光曝晒情况，并应用皮肤弹性测量仪测量外眦部、鼻唇沟及眶下皮肤弹性参数，包括：弹性，黏弹性，可扩展性和张力参数。比较不同年龄组间、市区与郊县组间各弹性参数间的差异。结果市区和郊县各弹性参数均与年龄有较好的相关性，随年龄增长，皮肤各弹性参数均下降。郊县组与市区组比较，弹性和黏弹性参数差异较小，而可扩展性和张力参数差异较大。结论弹性和黏弹性参数可能与内在老化有关，而可扩展性和张力参数可能与光老化有关。     

Oxytalan, elaunin, and elastic fibers in the human skin.

The elastic system of normal human skin was studied by light and electron microscopy. By light microscopy three different types of fibers were observed: oxytalan, elaunin, and elastic. The most superficial ones (oxytalan fibers) are very thin and directed perpendicularly to the dermoepidermal junction. They start from a plexus with the tinctorial characteristics of elaunin fibers which is connected with the thicker elastic fibers of the reticular dermis. At the electron microscopic level the oxytalan fibers are formed by bundles of tubular microfibrils 10 to 12 nm in diameter. In the deepest layers of the dermis an amorphous material is seen in the core of these bundles. In the elaunin fibers the amorphous material is sparse, while in the elastic fibers it is abundant and compact.