Wang Peng,Zhang Hongyan,Sha Ou,Guo Ruoxi,Zhang Han ,Zhang Lei

Tianjin Shangmei Cosmetics Co.,Ltd.,

Abstract This paper briefly introduce the test method for human evaluation of cosmetics to delay skin aging,and provide reference for the test of relevant indexes.By formulating a reasonable test plan and choosing appropriate equipment to test the improvement of the skin aging characteristics before and after the product is used,it can provide a scientific basis for claiming the effect of delaying skin aging.

Key words delaying skin aging;efficacy evaluation;cosmetics

How to keep the skin young is the common demand of all beauty lovers.Therefore,delaying skin aging has become the focus of modern cosmetics research and development.Skin aging is mainly determined by endogenous factors ( genetic factors or other irresistible factors ) and exogenous factors(ultraviolet radiation,smoking,wind,contact with chemicals,gravity,nutrition,lifestyle,etc.).The external characteristics of skin aging are mainly reduced skin moisture content,dull skin,pigmentation,dry and rough surface,loose skin,reduced elasticity and wrinkle formation,etc[1,2].Delaying skin aging effect or anti-aging effect is a commonly used word in cosmetic efficacy claims,but it is not in the classification code catalog of cosmetic efficacy claims.The delaying skin aging effect declaration of skin is a relatively complicated concept,which is related to the cosmetic efficacy declaration classification coding catalogue of whitening,sun protection,nourishing,repairing,moisturizing,anti-wrinkle,firming and other effects are related.

The human efficacy evaluation methods of cosmetics for delaying skin aging include subjective evaluation method and objective instrument evaluation method,which are both used to evaluate the influence of cosmetics on skin aging characteristics.The subjective evaluation method is to evaluate or score the skin moisturization,skin color change,wrinkle improvement effect,skin firmness and skin elasticity of the samples before and after use by volunteers or researchers according to certain evaluation criteria.This evaluation method is simple and easy,the operation does not require complex equipment,but requires a certain amount of training by the volunteer team or professional training by the researchers,so that the test results can be repeated to ensure the credibility and scientificity[3].This paper mainly introduces the objective instrument evaluation method in the evaluation method of declaring the efficacy of delaying skin aging.

1 Test method for firming efficacy

The interpretation of the firming effect is to help maintain the firmness and elasticity of the skin.The principle of the firming effect measurement mainly includes the suction method,the pressure method,the torsion method and the method of measuring the propagation speed of elastic shear force wave[4].

The test principle of suction method is based on the principle of suction and tension,the skin is sucked into a specific test probe by loading the negative pressure.The probe has a non-contact transmitter and receiver optical test system,which can measure a curve of the relationship between skin displacement and time,and represent the skin related parameters.Common test instruments such as MPA580-Cutometer(2 mm probe,Courage+Khazaka,Germany),the most common evaluation reference values are R2 and F4[5].R2 is considered to be the parameter value closest to the real state of skin elasticity,which is the ratio of rebound displacement Ua to the maximum tensile displacement Uf,that is,the ratio of the total elasticplasticity of the rebound part to the total elasticplasticity of the tensile part.The closer the value is to 1,the better the skin elasticity is.F4 is the area value in the envelope curve formed during the process of applying negative pressure and eliminating negative pressure during all test cycles (model 1 at least 10 cycles).The smaller the value is,the tighter the skin will be.Other indicators such as R0,R5,R7,R9,Q1,Q2 also have certain reference value for the study of delaying skin aging.There is also an instrument that uses negative pressure and displacement changes during recovery to test skin elasticity,which is based on the principle of lattice video displacement measurement of negative pressure and single image.The probe provides a constant negative pressure for the skin at the test site.In this process,the skin is pulled up by the negative pressure,and then the negative pressure is completely cancelled to restore the skin to the original state.The high-resolution CCD camera in the probe records the displacement changes of each pixel on the skin through the video Horm-Schunk optical flow algorithm,and obtains the deformation diagram of the vertical displacement curve of the skin.Some parameters related to skin viscoelasticity can be obtained through the skin deformation diagram.This method provides a new method for detecting skin viscoelasticity and anisotropy.The representative instrument is:Skin Viscoelasticity Tester CutiScan CS100.

The testing principle of the pressure method(indentation method) is based on the Yang’s modulus of elasticity.The mechanical properties of this elastic object are the physical quantities that characterize the tensile or compressive resistance of material within the elastic limit.The object deforms under the action of external force,when the external force is removed,the corresponding deformation disappears,which is an elastic deformation.The physical measurement of the resistance of the object to the shape change under the action of external force is proportional to the elastic modulus describing the elastic properties of the object.E = σ / ε,In the formula,σ is the positive stress,ε is the positive strain,and E is the Yang’ s elastic modulus.The larger E is,the smaller the deformation of the characterization material is when it is compressed or stretched.Representative instrument using this principle is as follows:Delfin skin elasticity measuring instrument ElastiMeter,Finland.Torsion skin elasticity tester is to stick a central plate with tape on the surface of skin,and stick another ring on the central plate,so as to determine the skin part of the test,and apply a torque to the center through the probe.The detection device accurately tests the rotation angle of the central plate after a torque is applied to test the elasticity of the skin.Torque skin elasticity tester can be used to evaluate the elasticity and friction performance of skin stratum corneum,and can test the elasticity performance of skin layers at different depths.The representative instrument using this principle is as follows:British Diastron skin tester Dermal Torque Meter DTM310.The method of measuring elastic shear wave propagation velocity can also test the viscoelasticity of skin.In addition,the skin and tissue biomechanical properties (softness)measurement analyzer BCT2000;the resonance vibration method skin softness test system Venustron;the stretching method skin elasticity tester Extensometer;BLS700 Ballistometer and other equipment can also provide scientific basis for skin tightening claims.

2 Test method for anti-wrinkle efficacy

The interpretation of anti-wrinkle effect is to help slow down the generation of skin wrinkles or make wrinkles become inconspicuous.The number,length,volume,area,depth of wrinkles and other comprehensive indicators of physical and chemical are important to measure the degree of skin aging,including three-dimensional imaging analysis method,two-dimensional image analysis method,profilometer measurement method and so on.

The wrinkle parameters obtained by using threedimensional skin rapid imaging system and computer processing images are commonly used in anti-wrinkle test,which have many advantages such as fast,stable,accurate,reliable and high resolution.The common image acquisition method is using image acquisition instrument to obtain three-dimensional image of skin under fringe light projection,such as Primos,a skin fast optical imaging system of LMI company in Canada.The 3D digital face VisioSphere 3D,skin fast optical imaging system EvaSKIN ( focusing on local test ) and EvaFACE ( focusing on full face test ) of EOTECH Company in France,in which the diagonal of EvaSKIN shooting area reaches 125 mm length,and the diagonal of EvaFACE shooting area reaches 300 mm length.In addition,the multi-functional skin imaging analysis system C-Cube of Pixience,France,is a portable integrated system for 3D measurement through photometric stereometry.Multifunctional 3D skin imaging analyzer Antera 3D from MIRAVEX LTD,Ireland.Derma TOP Visio-3D,a skin optical imager made by Breuckmann,Germany,can measure skin texture and wrinkles quickly,stably,accurately and reliably.3D imaging analysis method is more convenient for human-computer interaction and intuitive image analysis.

Application of facial image analyzer VISIA or VISIA-CR,spectral imaging blood flow analyzer TiVi700 ( wrinkle analysis software package ) and other equipment in the standard light or polarized light photographs,with Mirror Photo Tools,FrameScan,Image-Pro Plus professional image management and analysis software can get the relevant wrinkle parameters.The profilometer measurement method can also obtain the relevant parameters of skin wrinkles and realize the quantitative analysis of wrinkles.The methods include laser skin contour measurement,optical skin contour measurement,perspective skin contour measurement and mechanical skin contour measurement[6].This method requires the preparation of silica gel replication model on the skin surface,with the help of CCD camera and computer image processing system,the commonly used instruments are Visioline VL650,a skin wrinkle tester from CK,Germany.The wrinkle resistance test instrument can also be used for the analysis of skin surface texture.

3 Test method for skin roughness

Dry and rough skin surface is one of the characteristics of skin aging.Skin friction,roughness,smoothness and other indicators are important parameters to measure the degree of skin dryness and roughness.Common instruments include Frictiometer FR700,a skin friction test probe of CK,Germany.Its principle is that when the friction head of the Teflon material cylinder rotates,due to the effect of skin surface friction,the rotation speed of the cylinder will change.The smoother the skin of the tested part is,the smaller the torque required for the rotation of the motor is,and the smaller the skin friction value is.The friction value of the dry and wrinkled skin is relatively high,which can be used to measure the dynamic friction coefficient of the skin.The skin surface texture testing system VisioScan VC20plus uses a uniform ring-shaped ultraviolet(UVA) illumination source and a dermatoscope composed of a black and white high-resolution CCD camera to take images of the skin surface.The image is displayed in 256 black and white gray levels,wrinkles are displayed as dark black in the image and the peeled stratum corneum is displayed as bright white.The gray level distribution of the skin surface can be statistically analyzed by the active skin surface analysis software SELS,and the four parameters of clinically useful skin smoothness SEsm,skin roughness SEr,skin exfoliated cuticle level SEsc and skin wrinkles SEw are obtained.It is a simple,economical and accurate method for cosmetic efficacy test to directly photograph the active skin surface and analyze the skin surface morphology,skin roughness and drying degree through this unique high-resolution UV photography system.

4 Test method for skin structure

Skin aging and its physiological structure will also change.Ultrascan UC 22 (German C&K),a skin ultrasound diagnostic instrument,can test highresolution images of the skin at a depth of 8-10 mm using a 22 MHz ultrasound frequency,and can analyze skin thickness and skin transection.The area of the face,the degree of skin aging,etc.Denmark Cortex Dermalab Combo's high-frequency ultrasound probe or DermaScan C professional high-frequency skin color ultrasound system can also complete the relevant tests.This noninvasive detector based on ultrasonic imaging technology can be used to analyze the degree of skin aging and evaluate the efficacy of cosmetics.In addition,the skin multiphoton tomography system MPT flex (skin CT) can also test skin structure.MPT flex is a skin optical biopsy multiphoton tomography system that uses nearinfrared femtosecond laser technology with submolecular spatial resolution,which can be used in skin aging research.

5 Other methods

The moisturizing,sunscreen,freckle whitening,nourishing and repairing effects of cosmetics play an important role in delaying skin aging.The water content of healthy skin stratum corneum is 10 %～30 %.Adequate water is one of the important factors to maintain skin health and delay skin aging.If the water content of stratum corneum is too low,the skin will become dry,rough and prone to fine lines.The changes in the moisture content of skin keratinocytes before and after the use of the product can indirectly evaluate the efficacy of the product in delaying skin aging[7].Skin aging is a natural process determined by genetic factors and environmental factors.Longterm repeated irradiation of ultraviolet rays in sunlight is the most important factor affecting skin aging in environmental factors.Therefore,the use of sunscreen products is an important step to delay skin aging.After skin aging,pigment disorders,skin color will be yellow and dark,color spots or senile plaques.Evaluation of skin color changes,melanin content,number and area of color spots can indirectly evaluate the anti-aging effect of products.In addition,it is also an important reference point for delaying skin aging evaluation to provide nourishment for the application site and help maintain the normal state of the application site.

6 Conclusion

Skin aging involves changes in a variety of indicators,including:skin stratum corneum moisture content,transdermal moisture loss,skin firmness,skin elasticity,skin wrinkles,skin roughness,skin color,skin thickness,etc.The objective instrument evaluation method of delaying skin aging is the comprehensive test and scientific analysis of these indexes before and after using the product.With the promulgation and implementation of new cosmetics regulations,as well as the development of science and technology,the efficacy evaluation methods of cosmetics will continue to be updated,more scientific,rigorous,economical,efficient and reasonable,and providing sufficient scientific basis for the efficacy claims of cosmetics.