Pierre Agache

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.

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.

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.

The tetracyclines in dermatology

Tetracycline is one of the most widely used antibiotics. It may share some properties with conventional immunosuppressive drugs and act as an anti-inflammatory agent in the treatment of inflammatory disease. This article reviews cutaneous diseases that have been treated with tetracyclines and their antiinflammatory and immunosuppressive properties.

Sebum and stratum corneum lipids increase human skin surface free energy as determined from contact angle measurements: A study on two anatomical sites

Abstract Skin surface wettability is an important factor of the skin protective function, e.g. ecosystem preservation, smoothness and resiliency, barrier to chemicals, but surprisingly it has received little attention. Hence, this work aimed at calculating the surface free energy components of human skin, on the volar forearm, a sebum-poor area, and on the forehead, a sebum-rich area, and at assessing the influence of skin lipids on surface wettability using advancing contact angle measurements of water, glycerol, formamide and diiodomethane. Contact angles on the forearm and the forehead of ten healthy volunteers were measured, using a surgical microscope fitted with a slanted mirror and equipped with a video camera linked to a computer. Both skin areas were examined before and after ether treatment. According to the approach of van Oss et al. to solid-liquid interfacial interactions, the surface free energy components, i.e. Lifshitz-van der Waals, electron acceptor and electron donor components, were calculated. From the contact angle measurements and calculations of surface free energy, the forearm skin surface was found to be an almost apolar surface and the forehead skin surface a monopolar basic surface (electron donor). Ether treatment caused both surfaces to become more apolar, mostly by reducing the electron donor component. These results would suggest that skin surface lipids, mainly sebum, give the skin surface a hydrophilic character. However, no correlation was found between the skin lipid level and the basic component level which raises the question of the mechanism of the obvious wetting-enhancing effect of sebum. This could be due to the free fatty acids, which are especially abundant in the sebum.

Intestinal permeability in patients with psoriasis

A possible relationship between intestinal structure and function in the pathogenesis of psoriasis has recently brought about considerable interest. The purpose of this study was to evaluate the intestinal permeability in psoriatic patients by comparing it with healthy controls. 15 psoriatic patients and 15 healthy volunteers entered the study. Intestinal permeability was evaluated using the 51Cr-labeled EDTA absorption test. The 24-h urine excretion of 51Cr-EDTA from psoriatic patients was 2.46 +/- 0.81%. These results differed significantly from controls (1.95 +/- 0.36%; P less than 0.05). The difference in intestinal permeability between psoriatic patients and controls could be due to alterations in the small intestinal epithelium of psoriatics.

Changes in sebum levels and skin surface free energy components following skin surface washing

Abstract The forehead skin sebum casual (or usual) level, which is remarkably stable in a given individual, is responsible for the monopolar basic character of the skin surface. However, the significance of this finding, in terms of the physicochemical behaviour and wettability of the skin surface, remains unexplained. How does this vary during sebum casual level restoration following skin washing and what is its relationship with so-called “dry skin”? The present work was aimed at answering these questions. Forehead surface free energy components were assessed before and during the sebum casual level restoration following skin washing by nonionic soap and water, in 12 healthy volunteers: four oligo- (OS), four normo- (NS), and four hyper-seborrheic (HS) skins. Skin contact angles of water, formamide and diiodomethane were measured at intervals, and surface free energy components (i.e. Lifshitz–van der Waals, electron acceptor and electron donor components) were calculated using the contact angle values and acid–base theory of C.J. van Oss et al. The results showed that a low sebum-level does not deprive the skin surface of a normal Lifshitz–van der Waals component. This suggests that a low sebum-level is sufficient to render the skin normally lipophilic. The very low acidic component of the skin surface seemed to be due to the masking of acidic moieties by adsorbed water. The basic component was sebum-level dependent below a threshold value and remained to be related to the sebum free fatty acids and especially to their outward carboxylic group orientation. We conclude that the wetting properties of the skin surface could be defined by a “surface free energy component balance” or SEB. The SEB of NS and HS skins was around 0.22, and that of OS skin was 0.07. This low SEB stems from a weak hydrophilic component, allowing OS skin to be called dry skin, or better, a dry skin surface. This approach may provide a new insight into so-called “skin hydration”.

A new method to measure in vivo human skin hydrophobia.

Until now, the wettability of the skin has been only estimated through the measurement of its critical surface tension (Zisman), or surface free energy. These methods give information on the behaviour of the surface with water, but cannot quantify its behaviour with other polar liquids.

Assessment of the Water Content of the Stratum corneum Using a Sorption-Desorption Test

Background/Aim: Various instruments based on electrical properties of the skin are currently used to assess the stratum corneum (SC) hydration state or water holding capacity. However, no direct relation with the quantity of water measured is provided. The objective of the present study was to calibrate the Corneometer, a device displaying electrical-capacitance-related values (which reflect the skin hydration state), and the amount and behaviour of the water taken up by the outer part of the SC during a sorption-desorption test. Methods: The experiment was performed on the ventral forearms of 20 healthy volunteers after a rest in an environmentally controlled room. Corneometer and transepidermal water loss (TEWL) values were measured at intervals over the desorption process. The areas under the TEWL-versus-time curve provided the absolute amounts of residual sorbed water. Results: The decrease kinetics of both signals after subtraction of prehydration values were very similar and bi-exponential, both showing a rapid, then a slower phase. The absolute amount of water taken up by the SC (hygroscopicity) and the two desorption rates were obtained. The Corneometer values were mono-exponentially related to the amount of water remaining within the SC. This allowed the in vivo calibration of the Corneometer in terms of absolute amount of water over the desorption range. Conclusion: The method may be used to calibrate in vivo other electrical devices aimed at assessing SC hydration during a sorption-desorption test. It may also provide new ways to measure SC water uptake and water holding capacity following application of products.

Treatment of psoriasis with a new micronized 5-methoxypsoralen tablet and UVA radiation

Since 1974, phototherapy with psoralen and ultraviolet A (UVA) has been used successfully for the treatment of psoriasis. However, undesirable side effects, including phototoxicity, nausea, stomach pain and headaches, have led investigators to develop new psoralen compounds. 5-Methoxypsoralen (5-MOP) has thus been introduced as an alternative to 8-MOP because of its less pronounced side effects. Since the absorption kinetics and bioactivity of 5-MOP are known to be variable, a new micronized tablet form (5-MOPm) has been developed. In an open randomized study, oral treatments with 5-MOP or 5-MOPm plus UVA radiation were compared in 22 psoriatic patients. Skin type and initial psoriasis area severity index did not differ significantly between treatment groups. Serum concentrations were significantly higher (320 vs 85.82 ng/ml) and occurred earlier (51.8 vs 229.09 min) with 5-MOPm. In addition, a reduction in PASI of more than 90% was achieved sooner (10.63 vs 17.27 treatments) and with a lower cumulative UVA dose (145.89 vs 232.11 J/cm2), in the group treated with 5-MOPm. No side effects were observed with 5-MOPm. Our data indicate that 5-MOPm has a higher bioavailibility, clinical efficacy and tolerability than the commonly used 5-MOP.