J. de Rigal

Mechanical Properties and Young's Modulus of Human Skin in Vivo

SummaryThe mechanical properties of the in vivo dermis were measured by means of a torque applied to the skin. The resulting deformation of 2–6°, including the immediate and delayed visco-elastic components, as well as the relaxation were measured, and the raw values corrected for a constant skin thickness. The experiment performed on 138 individuals from 3 to 89 years old revealed a diminished elasticity and stretchability after the age of 30, associated with an increase in the visco-elastic component. The Youngs modulus doubles with age. The results are discussed in terms of the various models proposed to explain dermal structure.ZusammenfassungDie mechanischen Eigenschaften der Haut in vivo wurden anhand eines Drehmoments gemssen. Die so erhaltene Deformierung (2 und 6°), ihre sofortige und ihre viskoelastische verzögerte Komponente, sowie ihre Erschlaffung wurden gemessen und für eine konstante Hautdicke korrigiert. Der Versuch betraf 138 Personen im Alter von 3 bis 89 Jahren und zeigt eine Verminderung der Elastizität und der Dehnbarkeit mit Erhöhung der viskoelastischen Komponente nach 30 Jahren. Das Youngsche Modul verdoppelt sich mit zunehmendem Alter. Die Ergebnisse werden in bezug auf die verschiedenen Hautstruktur Modelle diskutiert.

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

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 womens skin becomes thinner than mens 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.

In vivo Biophysical Characterization of Skin Physiological Differences in Races

The role of race in modulating skin responses has been investigated. Several parameters (skin thickness, transepidermal water loss, water content of the stratum corneum and skin biomechanics) have been measured using noninvasive tools in whites, Hispanics and blacks to assess whether the melanin content could induce changes in skin biophysical properties. Marked differences between races appear in stratum corneum water content and in skin extensibility, recovery and elastic modulus. Measurements done in different sun-exposed sites highlight the effects of solar irradiation on the skin and the role of melanin in preventing skin damage. The study shows that racial differences in skin physiology exist and are mainly related to the protective role of melanin present in races with darker skin. Moreover, differences in skin hydration are not fully explained according to the site and presence of hair.

Influence of ageing on the in vivo extensibility of human skin at a low stress.

SummaryThe response of the forearm skin to a 9 · 10-3 N · m torque was measured on 141 subjects aged 3–89 years. The results for each age class were ajusted to a skin thickness of 1 mm by use of a skinfold caliper. Results indicate a maximum skin thickness around the age of 40 years. Standardised skin extensibility decreases with age, the skin of females being less extensible than that of males. These results, which should be considered in relation to the total water content of the skin, are compared to those of other papers dealing with this subject.ZusammenfassungBei 141 Personen im Alter von 3 bis 89 Jahren wurde die Reaktion der Haut auf ein Drehmoment von 9 · 10-3 N · m gemessen. Für jede Alterstufe wurden die Ergebnisse mit Hilfe eines “Skinfold Caliper” für 1 mm Hautdicke errechnet. Die maximale Hautdicke besteht im Alter von etwa 40 Jahren. Die Dehnbarkeit der Haut nimmt mit zunehmendem Aler ab. Diese Ergebnisse, die im Zusammenhang mit dem Gesamtwassergehalt der Haut betrachtet werden sollten, werden mit den Ergebnissen aus der Literatur verglichen.

How Does Sodium Lauryl Sulfate Alter the Skin Barrier Function in Man? A Multiparametric Approach

The effects of topically applied sodium lauryl sulfate were studied in vivo, in man, through noninvasive methods and compared with those obtained in vitro, using human stratum corneum as a model. The results show that the very marked increase of transepidermal water loss obtained in vivo cannot be related to any removal of epidermal lipids. The most likely explanation of our findings lies in the hyperhydration of stratum corneum consecutive to the inflammation process and a possible disorganization of the lipid bilayers.

In vivo Cross-Sectional Ultrasonic Imaging of Human Skin

This paper describes a new experimental set-up allowing routine cross-sectional ultrasonic images of human skin to be obtained in vivo and presents the first high-resolution images it gives. This system is characterized by the utilization of damped, high-frequency ultrasonic transducers. This type of transducer is longitudinally driven along the skin by a stepping motor under the control of a computer, which at the same time stores the digitized reflected signals. After the acquisition sequence, the image of the skin is displayed on a video monitor after data processing of the ultrasonic signals. On the images thus obtained, fascia, hypodermis, reticular dermis, pilosebaceous units, and adventitial dermis can be visualized. Due to a lack of resolution (about 80 microns) epidermis can only be viewed on certain zones like the hand.

An in vivo assessment of the biomechanical properties of human skin modifications under the influence of cosmetic products.

A new device using a torsional technique has been developed to record the biomechanical properties of the skin.

Are corneocytes elastic

By using a microhandling system, we have recorded the force necessary to elongate isolated corneocytes. According to certain hypothesis, it appears that the elastic modulus of corneocyte is far higher than that of stratum corneum itself. Aggregates of corneocytes are disassembled by forces with a wide range of intensity. In the light of these experiments, stratum corneum appears as a very supple material where the deformations occur more by a plastification of the intercellular medium and an unfolding of the microrelief lines than an elongation of the corneocytes themselves. Moreover, desmosomes remnants could play a certain role in the corneocytes cohesiveness.

Effect of topical corticosteroids on human sebum production assessed by two different methods

SummaryTopical corticosteroids are widely used in cutaneous diseases. Although their mode of action on different skin compartments has been documented, little is known about their effects on the human sebaceous gland. We investigated the effects of two corticosteroids of differing potency on the excretion of sebum by means of two validated techniques: the Sebutape and the Lipometre. This study was conducted on the forehead skin of normal healthy subjects. The results obtained with both techniques correlated well. The application of both corticosteroids during a 4-week period led to a significant decrease in sebum excretion. This decrease was more pronounced with the more potent corticosteroid (Dermovate). In the light of these findings, it is likely that topical corticosteroÏds exert an anti-proliferative action upon the sebaceous cells in a similar manner to their effect in other skin compartments

New experimental approach to measure the skin-reflected light. Application to cutaneous erythema and blanching.

By modifying the blood supply in the upper part of the dermis, the colour of the skin is changed by any material in contact with it. This is a great difficulty when we want to measure the colour intensity in erythema or blanching. To avoid this problem, we designed and built a device which measures the skin reflectance value without any contact with the skin. The use of this device on man to study the skin blanching after application of dermocorticoids allows us to determine the more potent drug among a series (clobetasol propionate) and, for a given drug (betamethasone), the more efficient preparation (oil-in-water emulsion). The study of the effect of increasing irradiation doses of ultraviolet light show that the sensitivity of the device is equivalent to that of the clinical assessment and that the relationship between the irradiation dose and the skin reflectance is sigmoidal.