Correlating Aging with Skin’s Mechanical and Optical Properties

May 1, 2014 | Contact Author | By: Olga Freis, PhD, Gilles Perie and Andreas Rathjens, BASF Beauty Creations/Care Solutions, Pulnoy and Essey-lès-Nancy, France
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Title: Correlating Aging with Skin’s Mechanical and Optical Properties
biomechanical propertiesx optical propertiesx brilliancex colorx fluorescencex
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Keywords: biomechanical properties | optical properties | brilliance | color | fluorescence

Abstract: The aim of this study was to monitor the evolution of biomechanical and optical properties of the skin with aging. Different biophysical parameters were measured, including skin: elasticity and firmness, color, brightness, fluorescence emission, sebum content, hydration and pH. A significant evolution of the evaluated parameters with aging was observed.

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O Freis, G Perie and A Rathjens, Correlating Aging with Skin’s Mechanical and Optical Properties, Cosm & Toil 129(4) 66-75 (May 2014)

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The evolution of skin’s biomechanical and optical properties as a function of aging and/or photoaging is one of the main targets of cosmetic and dermatological research. Many noninvasive devices to measure skin’s biomechanical properties have been developed using alternative methods such as stretching, torsion, indentation and suction. Measurements of skin deformation after suction or torsion are the most widely used techniques in cosmetic research.

The skin’s optical properties play an important role as well, and devices measuring these characteristics assess reflected light after illumination of the skin surface. Different noninvasive methods have been proposed for evaluating skin complexion in vivo. These include quantitative measurements of skin color, using colorimetry—i.e., L*a*b* and Individual Typological Angle (ITA°); or of the intensity of specular reflection and the back-scattering of light from the skin. The purpose of this study was to demonstrate the evolution of the measured parameters with aging, and to find the correlation between measured mechanical and optical properties of the skin.

Methods

Test population and body sites: A total of 113 female volunteers ages 18–76 participated in the study. All participants were Caucasian, with no apparent signs of skin disease. The volunteers applied no cosmetic products for 24 hr before measurements were taken. Measurements were conducted on two different anatomical regions: the inner forearms and/or the face, i.e., the forehead, temples or cheeks.

Biomechanics: The biomechanical properties of the skin were measured using commercially available standard devices as well as an internally developed device, referred to as a corneovacumeter. The corneovacumeter measures capacitance between skin and a conductive plate, whereby capacitance is proportional to skin deformation. With this type of device, 12 simultaneous suctions are realized and the result provided is the mean of the measurements. While such suction-based devices measure vertical skin deformation after suction, torque-based devices measure deformation after torsion. For the present study, both standard and surface methods were used for calculating biomechanical skin parameters.

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Table 1. Correlation Coefficients of Three Biomechanical Properties Devices

Table 1. Correlation Coefficients of Three Biomechanical Properties Devices

The best and highly significant correlation was obtained on the skin firmness parameter, Ur/Uf.

Table 2. Correlation Coefficients Between Skin Color (L*, ITA°) and Brightness

Table 2. Correlation Coefficients Between Skin Color (<em>L*</em>, ITA°) and Brightness

A strong positive correlation was found between the diffuse reflection and colorimetric parameters L* and ITA°.

Table 3. Correlation Coefficients Between Skin Color, Brightness and Fluorescence

Table 3. Correlation Coefficients Between Skin Color, Brightness and Fluorescence

A positive correlation was observed between the skin complexion, evaluated by L* and ITA° measurements, and epidermal turnover. Higher epidermal turnover resulted in higher values for skin complexion. On the contrary, the accumulation of AGEs with age correlated negatively with skin complexion values.

Table 4. Correlation of Mechanical and Optical Skin Properties

Table 4. Correlation of Mechanical and Optical Skin Properties

The correlation between mechanical and optical properties; the statistical comparison demonstrates there are significant correlations between the skin firmness parameter, R7, and optical properties linked to radiance, such as color and brightness. A negative correlation was found between the viscoelasticity of skin, R6, and skin radiance, characterized by luminance and specular and diffuse reflection. The correlation between elasticity of the skin, R5, and optical parameters was weaker and less significant.

Figure 1. Cutometer results

Figure 1. Cutometer results

The obtained skin deformation curves were similar for all devices, and on the basis of the deformation curves, the biomechanical parameters were calculated

Figure 2. Corneovacumeter results

Figure 2. Corneovacumeter results

The obtained skin deformation curves were similar for all devices, and on the basis of the deformation curves, the biomechanical parameters were calculated

Figure 3. Dermal torquemeter results

Figure 3. Dermal torquemeter results

The obtained skin deformation curves were similar for all devices, and on the basis of the deformation curves, the biomechanical parameters were calculated

Figure 4. Evolution with age of parameters linked to skin color—luminosity (L*) and ITA°

Figure 4. Evolution with age of parameters linked to skin color—luminosity (<em>L*</em>) and ITA°

Colorimetry measurements of luminosity and ITA° revealed a statistically significant evolution of parameters with age, and the diminution observed related to both UV exposed and non-exposed skin on the cheeks and forearms.

Figure 5. Evolution with age of the parameters linked to skin color

Figure 5. Evolution with age of the parameters linked to skin color

Evolution with age of the parameters linked to skin color—luminosity (L*), ITA°, skin redness and yellowness on the cheeks, as evaluated from macrophotographs

Figure 6. Evolution with age of the parameters linked to the skin radiance

Figure 6. Evolution with age of the parameters linked to the skin radiance

Evolution with age of the parameters linked to the skin radiance—peak height and width in specular reflection, and peak height in cross light on the forearms and cheeks

Figure 7. Age-related diminution of tryptophan level on the forearms and face (temples)

Figure 7. Age-related diminution of tryptophan level on the forearms and face (temples)

The authors could conclude that photoaging as well as intrinsic aging reduced cell renewal.

Figure 8. Evolution of normalized fluorescence intensity with age for collagenase digestible collagen crosslinks on the forearms and face (temples)

Figure 8. Evolution of normalized fluorescence intensity with age for collagenase digestible collagen crosslinks on the forearms and face (temples)

The fluorescence of collagen and elastin cross-links increased with age on the forearms and face (temples), indicating an accumulation of AGE.

Figure 9. Evolution of sebum excretion on forehead as a function of age

Figure 9. Evolution of sebum excretion on forehead as a function of age

Sebum excretion was strongly dependent on the age of volunteers, with a significant decrease in the group of post-menopausal volunteers observed.

Footnotes [Freis 129(4)]

a Cutometer SEM 575, Courage & Khazaka
b Dermal Torquemeter, DiaStron
c CR 200, Minolta
d LS 55 Spectrofluorimeter, Perkin Elmer
e Derma Unit, Courage & Khazaka

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