Method to measure skin elasticity and firmness

Abstract

The invention relates to a method of measuring the elasticity and firmness of skin. The invention also relates to methods of measuring improvements in a person's skin health by measuring firmness and elasticity before, during and after a cosmetic treatment. The invention further relates to methods of measuring the improvement in a person's skin firmness and elasticity that a cosmetic agent may cause when applied on the skin.

Claims

1. A method of determining a skin elasticity value for a person's skin, comprising: (a)contacting two parallel metallic plates of a mechanical pinching system on a skin surface zone, recording a first thermal image of the skin surface zone that displays thermal prints of the metallic plates on skin with an infrared thermography imaging apparatus, and measuring a first distance between the two parallel metallic plates on the first thermal image, (b)after the recording of the first thermal image, pushing at least one of the two parallel metallic plates of the mechanical deformation system toward the other in a direction that is parallel to the skin surface, so as to pinch the skin between the two parallel metallic plates, under a controlled pressure, wherein the two parallel metallic plates remain parallel during the pushing, (c)releasing the controlled pressure, (d)after releasing the controlled pressure, recording a second thermal image of the skin surface zone that displays thermal prints of the metallic plates on skin with the infrared thermography imaging apparatus, and measuring a second distance between the two parallel metallic plates on the second thermal image, and (e)determining a skin elasticity value associated with an elastic recovery of the skin, said skin elasticity value corresponding to the ratio between the second distance and the first distance.

2. The method of claim 1, wherein in (b), the controlled pressure is between 20 and 40 N.

3. The method of claim 2, wherein the skin is considered as having elasticity when the skin elasticity value is higher than 1.

4. The method of claim 1, wherein the mechanical deformation system comprises an internal spring and two metallic plates attached to two sliding sections.

5. A method for measuring the effect of a cosmetic product on improving the firmness or elasticity of a person's skin, said method comprising: calculating a first value associated with an elastic recovery of the skin sample according to the method of claim 1, applying the cosmetic product on the skin sample, calculating a second value associated with an elastic recovery of the skin sample according to the method of claim 1, and comparing the first value and the second value.

6. The method of claim 1, wherein the skin elasticity value corresponds to at least one of determining firmness, tonicity, suppleness, sagging skin, oval of the person's face, bags beneath the person's eyes, nasolabial folds or ptosis of the lower part of the person's face.

7. The method of claim 1, wherein the method is conducted on skin of the person's face.

8. The method claim 1, wherein the method is conducted on a lower part of the person's cheek.

9. The method of claim 1, wherein the pushing of the at least one of the two parallel metallic plates toward the other narrows a space between the two parallel metallic plates; and deforms the pinched skin within the space between the two parallel metallic plates; wherein upon releasing the pressure, the pinched skin returns to an unpinched position.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 represents a pinching system that can be used according to the present invention.

(2) FIG. 2 gives an example of the positioning of the pinching system on the cheek. Skin is trapped between the two metallic parts of the pinching apparatus.

(3) FIG. 3 is an image of the face obtained by infrared thermography, once the metallic parts of the pinching system has been placed on the surface of the skin face before pinching.

(4) FIG. 4 gives the description of the different skin pinching steps: Step a: Positioning of the system Step b: Pinching of the skin Step c: Stop pinching the skin by releasing the system.

(5) FIG. 5 represents the trend in the AP/AV distance ratio as a mean of 3 experts' estimation, as a function of age.

DETAILED DESCRIPTION OF THE INVENTION

(6) The subject of the present invention is a novel instrumental method using infrared thermography imaging coupled with a mechanical deformation system of the skin. This method is useful for characterizing rheological properties of the skin.

(7) According to one of its aspects, the invention deals with a method of determining a skin elasticity value for the skin of an individual, said method using infrared thermography imaging coupled with a mechanical deformation system comprising at least two metallic plates intended to pinch a skin sample of a person.

(8) In a preferred embodiment, the method deals with determining the elasticity of skin face. In this embodiment, Elasticity as used in the context of the present invention may correspond to one or several clinical criteria such as firmness, tonicity, suppleness, sagging skin, oval of the face, bags beneath the eyes, nasolabial folds or ptosis of the lower part of the face. Such clinical criteria are usually estimated by the person him/herself, or by a dermatologist. They can be defined for example by using a graduated, validated, visual scale such as one described in Bazin, R., Doublet, E., In: MED'COM (Eds), Skin Aging Atlas, Volume 1 Caucasian Type, Paris, France, 2007, pp: 46-57.

(9) The volunteers' self-assessment was specifically quantified by the method of the invention, particularly as regards firmness, elasticity and skin sagging. The method of the invention is an interesting alternative to current subjective methods and enables to quantify the rheological properties of the skin. The method of the invention resolves the difficulty of measuring the subjective perception of the global phenomenon of skin firmness, elasticity and sagging. The inventors showed that the measurement performed with the method of the invention were consistent with the volunteers' subjective assessment of their skin's elasticity.

(10) According one embodiment, the method comprises the steps of acontacting the metallic plates of the mechanical deformation system with the skin sample and recording a first thermal image of the skin on which thermal prints of the metallic plates on skin can be displayed, bpinching the skin sample with the mechanical deformation system intended to trap said skin sample, and subsequently releasing the system, crecording a second thermal image of the skin on which thermal prints of the metallic plates on skin can be displayed, dcalculating a value associated with an elastic recovery of the skin sample.

(11) In step b, the pinching of the skin is preferably made under a controlled pressure being between 20 and 40 N, more preferably between 25 and 35 N, typically being 31 N.

(12) The metallic plates are preferably parallel so that contact between the metallic plates with the skin generates parallel markings displayed with infrared thermography imaging.

(13) The value associated with an elastic recovery of the skin sample corresponds to the ratio between a first distance corresponding to the distance between the thermal prints of the metallic plates measured after pinching in step c, and a second distance corresponding to the distance between the thermal prints of the metallic plates measured before pinching in step a.

(14) A visual reproduction of the deformation can be obtained using infrared thermography imaging ThermaCAM SC500PAL camera, FLIR System, Sweden. Once the system is removed from the skin after application, a thermal image of the face is usually recorded. The contact between the system's metallic bars (cold temperature) with the skin (warm temperature) generates clearly discernible markings. The distance (in cm) from the centre of each of the marks left on the skin is calculated. The same distance is also measured before pinching.

(15) To evidence rheological variations, the measurements of the distance separating the two imprints left by the system in the image are taken before (AV) and immediately after the restriction (AP), and the ratio of both distances
R=AP/AV distance
is calculated. This calculation can be made either manually by experts or using software.

(16) The closer this ratio is to the value of 1, the greater the rheological properties of the skin (increased elasticity and suppleness). If this ratio is low, the skin has reduced elasticity and suppleness.

(17) In one embodiment, the pinching system is formed by an internal spring and two metallic plates fixed to two sliding sections (FIG. 1).

(18) The two sections slide under a constant, controlled pressure of between 20 and 40, for example 31 N. To carry out measurements, the pinching system is placed at certain points of the skin surface in static position to set up contact with the metallic plates of the system. Then, using the fingers, the two outer parts of the system are pulled inwards as far as an abutment thus trapping part of the skin within the created space. The system is then relaxed to release the skin allowing it to return to its initial state.

(19) The mechanical deformation system can be placed at certain points of the skin surface in static position to set up contact with the metallic plates of the system.

(20) The method of the invention is preferably conducted on the face, more preferably on the lower part of the cheek.

(21) According to another aspect, the invention deals with a method of measuring the impact of various cosmetic products on improving the subjective perception of firmness.

(22) One object of the invention is a method for measuring the effect of a cosmetic product on improving the firmness or elasticity of the skin of a person, said method comprising: calculating a first value associated with an elastic recovery of the skin sample according to the method of determining a skin elasticity value previously described, applying the cosmetic product on the skin sample, calculating a second value associated with an elastic recovery of the skin sample according to the method of determining a skin elasticity value previously, comparing the first value and the second value.

(23) The invention is illustrated more in detail in reference to the following examples.

Example 1: Instrumental Evaluation According to the Invention and Correlation with Clinical Assessment

(24) 116 Caucasian women, allocated to 5 different age groups (group 20-29, n=20, mean=24.3+/3.1 years; group 30-39, n=23, mean=34.4+/2.8 years; group 40-49, n=23, mean=44.4+/3.0 years; group 50-59, n=24, mean=54+/3.1 years and the group 60-70, n=26, mean=64.9+73.4 years), were recruited for this study.

(25) AInstrumental Evaluation According to the Invention

(26) Study Protocol

(27) The volunteers were invited to sit down in a comfortable armchair in order to prevent any head movements during measurement. An infrared thermography camera set up a fixed distance away from the volunteer, was used to capture the image of the skin before and after mechanical deformation.

(28) Pinching System

(29) A system comprising an internal spring and 2 metallic plates fixed to 2 sliding sections was used for this study (see FIG. 1). To record the measurement, the pinching system was placed on the skin in a static position in order to create contact between the system's metallic plates and the skin. Then, using the fingers, the two outer parts of the system were pulled inwards as far as the wedge (the two sections slide at a controlled constant pressure of 31 N), thus trapping part of the skin within the space created (see FIG. 2). Finally, the two sections were relaxed thus releasing the skin and allowing it to return to its initial state (see FIG. 4).

(30) Infrared Thermography

(31) Skin deformation was analysed using an infrared thermography camera (ThermaCAM SC500PAL, FLIR SYSTEM, Sweden).

(32) A first thermal image was recorded before pinching (see FIG. 3).

(33) The contact between the system's metallic bars (cold temperature) with the skin (warm temperature) generates clearly discernible vertical and parallel markings. The distance (in cm) from the centre of each of the marks left on the skin is calculated.

(34) Once the system was removed from the skin after application after pinching, a second thermal image was recorded.

(35) The distance separating the two vertical prints on the image is measured before (AV) and immediately after (AP) the restriction and the ratio of both distances (R=distance AP/distance AV) is calculated.

(36) Two way analysis of variance (ANOVA) and linear regression were used to assess the effect of age. The correlations were studied on the basis of linear regression (two by two) and Principal Component Analysis (PCA). All of the statistical tests were analysed with a risk =5%.

(37) Repeatability and Reproducibility of the Method

(38) A study was conducted to verify the repeatability and reproducibility of the measurements. Three experts quantified the distances before and after pinching of the skin. Four photos were taken by panellists: 2 photos before pinching and 2 photos after pinching.

(39) The results clearly show that the measurements are fully repeatable and reproducible (see the Table I below).

(40) TABLE-US-00001 TABLE I Repeatability and reproducibility of the method Nominal Mean Maximum values variations (Sr) variations (r) Distance BEFORE pinching 2.62 0.05 0.14 AV (cm) Distance AFTER pinching 2.02 0.07 0.9 AP (cm)

(41) BResults According Age Groups

(42) The older the person, the more the rheological AP/AV index is reduced. The reduction of AP/AV index goes along with the loss of the skin's rheological characteristics (suppleness, elasticity) (see Table II and FIG. 5).

(43) TABLE-US-00002 TABLE II AP/AV ratios according to age groups 20-30 30-40 40-50 50-60 Signif. Expert 1 0.84 0.80 0.76 0.77 S (<0.01) Expert 2 0.81 0.77 0.75 0.75 S (<0.01) Expert 3 0.79 0.76 0.75 0.74 S (<0.01)

(44) Statistical analysis of the AP/AV distance ratio revealed a significant age-related correlation (r=0.23, p=0.02).

(45) C-Study on the Correlation of the AP/AV Index with Subjective Evaluation of Rheological Criteria

(46) The coherency between the measurements taken using the method of the invention (pinching combined with infrared thermography) and a subjective evaluation previously carried out has been verified.

(47) Volunteers' Self-Assessment and Clinical Evaluation

(48) Each volunteer was asked, in front of a mirror, to answer the self-assessment questionnaire (based on the information collected during the interviews), scoring each item on a scale of 1 to 10 (1 being the lowest score and 10 being the highest). All of the evaluations were carried out on skin without cream and make-up. Some of the evaluations were carried out in front of the mirror in order to record the extent of sagging skin in three areas using a graduated, validated, visual scale as described in Bazin, R., Doublet, E., In: MED'COM (Eds), Skin Aging Atlas, Volume 1 Caucasian Type, Paris, France, 2007, pp: 46-57, such as bags under the eyes, nasolabial folds and ptosis of the lower part of the face. A zero score denoted no visible presence of sagging whilst 10 indicated the highest level of sagging.

(49) The results are summarized in the Table below.

(50) TABLE-US-00003 TABLE III Volunteers' self-assessment Group Group Group Group Group 20-29 30-39 40-49 50-59 60-70 P value FIRMNESS F 7.5 .sup.A 6.6 .sup.B 6 .sup.BC 5.3 .sup.C 5.3 .sup.C S (p < 0.01) ELASTICITY E 7.6 .sup.A 6.6 .sup.B 6.5 .sup.B 5.4 .sup.C 5.3 .sup.C S (p < 0.01) SMOOTH APPEARANCE 6.6 6.3 6.1 6.3 6.7 NS OF THE SKIN MOISTURE PERCEPTION 5.4 5.2 5.7 5.3 5.3 NS SAGGING SKIN SS 1.1 .sup.A 2.9 .sup.B 4 .sup.C 4.8 .sup.D 5.3 .sup.D S (p < 0.01) OVAL OF THE FACE 8.7 .sup.A 7.3 .sup.A 6.3 .sup.B 5.2 .sup.B 5.2 .sup.C S (p < 0.01) FINE LINES 2.2 .sup.A 4.6 .sup.B 5.2 .sup.BC 6.4 .sup.CD 6.2 .sup.D S (p < 0.01) WRINKLES 1.4 .sup.A 3.5 .sup.B 5.3 .sup.C 6 .sup.CD 6.5 .sup.D S (p < 0.01) BAGS BENEATH THE 0.7 .sup.A 1.4 .sup.A 1.7 .sup.A 2.7 .sup.B 2.8 .sup.B S (p < 0.01) EYES NASOLABIAL FOLDS 0.7 .sup.A 0.9 .sup.B 2 .sup.C 3.3 .sup.C 3.5 .sup.C S (p < 0.01) PTOSIS OF THE LOWER 0.4 .sup.A 1.8 .sup.B 2.9 .sup.C 3.1 .sup.D 3.5 .sup.D S (p < 0.01) PART OF THE FACE Note: When there are significant differences between age groups for each item, letters indicate the age groups to which it belongs. If the groups have the same letter, they are comparable, if not they are they significantly different.

(51) The results have shown a marked reduction in the firmness, elasticity and oval of the face with age. Increased sagging of the skin is also clearly apparent with advancing age. As regards the analysis of the various visual grades, the results have shown a significant increase in value for the three facial areas studied (bags beneath the eyes, nasolabial folds and oval structure of the face). At the same time, fine lines and wrinkles are logically accentuated with age.

(52) A clinical evaluation was carried out by a dermatologist at the same time as the subjective self-evaluation. The same items than the ones listed in the self-assessment questionnaire, and the same visual scales for skin sagging were used for the clinical evaluation.

(53) The results of the clinical evaluation were very similar to those of the self-assessment except for perceived moisture levels, which fell significantly with age.

(54) Correlation of the AP/AV Index with Subjective Evaluation of Rheological Criteria

(55) Overall, the results clearly showed that the AP/AV ratio gives a coherent description of the subjective assessment made by women on the elasticity and firmness of their skin.

(56) Data analysis emphasized significant links with the volunteers' self-assessment for certain items and according to age (Firmness F: r=0.32, p<0.01; Elasticity E: r=0.28, p<0.01; Sagging skin SS: r=0.37, p<0.01).

Example 2: Study on the Efficacy of a Cosmetic Product

(57) A study on the efficacy of a cosmetic product was conducted over a period of 3 weeks in France in 40 individuals. The measurements were made on nude skin before and after 3 weeks' treatment. The treatment consisted in a twice-a-week application for 3 weeks of a product marketed under the trade name Masque RevitalisantDior Prestige de Christian Dior (mask in fabric).

(58) The AP/AV ratio was measured in the same conditions as described in Example 1. The results are reproduced in Table IV.

(59) Under the study conditions, the treatment allowed a significant improvement in the suppleness/elasticity of the skin as expressed by a significant increase in the AP/AV ratio.

(60) TABLE-US-00004 TABLE IV AP/AV ratio before and after a cosmetic treatment T0 T1 Before application After 3 weeks use (nude skin) (nude skin) P* time AP/AV ratio 0.745 0.764 S (<0.01) P* time was calculated with a risk of = 5%