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Efficacy Methodology and Assessment of Cosmetics
R. Randall WickettUniversity of CincinnatiCollege of Pharmacy
Outline of Topics• Non-invasive measurements of skin function
– Transepidermal Water Loss– Electrical Measurements– Mechanical Measurements– Skin Color– Surface Analysis
• Protocols for Efficacy Assessment– Moisturizer Efficacy– Cleanser Mildness– Anti-aging products
Utility of Non-invasive Bioengineering Measurements
• Why not just rely on visual grading?• Grading is not “objective”• Grading is not “reproducible” at an exact level.
Agreement within ± 0.5 grades units is considered very good.
• Bioengineering Tools can give additional information. For instance visual grades will not necessarily tell you if skin is more or less elastic or if the skin barrier is perturbed.
• Bioengineering measurements can be used to support claims and for guiding the product development process
• Training and experience are required to obtain valid and reproducible bioengineering measurements
Ronald Marks, M.D.
• One of the “Godfathers” of bioengineering measurement on skin
• Organized the first symposium on noninvasive methods and the skin in 1976 and founded ISBS
Albert M. Kligman, M.D.
• Another Godfather of Skin Bioengineering – first talked about the possibility of admitting a “blind person” as a dermatology resident.
• A fool with a tool is still a fool
General Considerations for non-invasive measurements on skin
• There are no published standard protocols similar to ASTM (American Society for Testing Materials)
• “Guidances” are published by EEMCO (European group on Efficacy Measurements of COsmetics and other topical products) for various categories of methods
General Recommendations for instrumental measurements on Skin
• Some control of testing environment is necessary to prevent sweating– Normally 20 ± 1 C, 30-45% RH
• Subjects should equilibrate 30 minutes if possible• Subjects should avoid drinking hot coffee or tea or
eating for at least 1 hour prior to measurement• Subjects should avoid uncontrolled use of cosmetic
products on the measurement sites for at least 1 week prior to measurement
• Subjects with any obvious skin disease, tattoos or injury in the treatment area will be excluded.
Transepidermal Water Loss
• Water transport through the skin by passive diffusion
• Rate is 5-10 g/m2/hr in healthy skin• Increases with surfactant damage• Used to measure occlusion by products• Used extensively in barrier disruption and repair
studies• Panelists must not be sweating. Equilibrate 30 min.
at ~21C RH<50%
The Dermalab Evaporimeter
The C+K devices
TEWA Meter probe
Corneometer probe
Sebumeter
Cutometer probe
The operating principle of open chamber TEWL devices
Forearm Controlled Application Test (FCAT)
• Lather wetted bar for 6 seconds with Masselin towel
• Transfer lather to site and wash for 10 seconds
• Leave lather in place 90 seconds• Rinse for 20 seconds• Repeat 4X daily for one week
Forearm washing
Washing and rinsing
Forearm wash test bars
• Bar 1 mild syndet + oatmeal
• Bar 2 mild syndet + oatmeal
• Bar 2 mild syndet
• Bar 4 Soap pure soap
• Bar 5 Soap + humectant
Measuring TEWL after a forearm wash test
TEWL: Forearm wash test
RR Wickett, Forearm wash testing of mild soap bars containing colloidal oatmeal, Canadian Chemical News, 49(1), 22-23 (1997).
Redness grade versus TEWL: Forearm Wash Test
Electrical Measurements of Skin
• Skin lipids have a low dielectric constant, water has a high dielectric constant.
• When skin is hydrated conductance and capacitance (reactance) increase and impedance decreases.
• Used to estimate water content of stratum corneum.
The NOVA DPM
The Skicon
Correlation with dry skin grades
• Dry skin is lacking in moisture.• Several studies have shown that electrical
measurements correlate with dry skin grades as expected
• Morrison and Scala correlated Correlated Corneometer and Skicon readings to flaking grades on dry hands scores that developed as subjects washed their hands for 1 minute five times a day for 4 days.
• We also have data on correlation of readings of all three instruments to dry skin grades on the legs.
Correlation between Flake Grade and Corneometer CM 820 values
Morrison and Scala(1996) J. Toxicol-Cut.& Ocular Toxicol, 15:305-314 15
Skicon versus mean flaking grade
Morrison and Scala(1996) J. Toxicol-Cut.& Ocular Toxicol, 15:305-314 15
Grading scale for dry skin, half grades are allowed
Grade Description
0 No scaling
1.0 Slight powdery appearance and occasional patches of small scales widely distributed
2.0 Small scales in combination with a few larger scales, slight roughness, whitish appearance
3.0 Small and large scales uniformly distributed, definite roughness and possible a few superficial cracks
4.0 Dominated by large scale, rough, redness present and eczematous changes
F Li, MO Visscher, E Conroy and RR Wickett, J. Cosmet. Sci. 52, 23-33 (2001).
Scatter plot of Skicon reading versus Dry Skin Grade
R. R. Wickett and F. Li Unpublished Data
Average values versus dry skin grades Skicon and Corneometer
R. R. Wickett and F. Li Unpublished Data
Average values versus dry skin grades NOVA meter
R. R. Wickett and F. Li Unpublished Data
Brancaleon et al. correlated Skicon readings with ATR-FTIR measurements of water in the SC. “Our attempt to link the hydration measured withATR-FTIR to the hydration measured with the Skiconhygrometer shows a high degree of correlation. This is not unexpected as both instruments record superficial hydration.”
Correlations among instrumental measurements
SKICON VS CORN
0
50
100
150
200
250
300
350
0 20 40 60 80
r =0.8741
NOVA VS SKICON
0
50
100150
200
250
300
350400
450
500
0 50 100 150 200 250 300 350
r =0.9347
NOVA VS CORN
0
50100
150200
250
300350
400450
500
0 10 20 30 40 50 60 70 80
r =0.8873
F. Li, et. Al J. Cosmet. Sci. 52, 13-22(2001).
Correlations between instruments
Clarys et. al. Fluhr et. al. Our work*
NOVA vs Skicon 0.96 0.96 0.93 NOVA vs. CM 0.97 0.82 0.87 Skicon vs. CM 0.89 0.83 0.89
Clarys, P., et al Skin Res Technol, 5, 14(1999).
Fluhr, J. W., et al Skin Res. and Technol., 5, 171 (1999).
Li, F. et al J. Cosmet Sci 52, 13-22 (2001)
Electrical measurements and moisturizer claims
• For more than 20 years electrical measurements made within 30 minutes to a few hours of treatment have been used to substantiate claims of moisturizing efficacy.
• We have reported that measurements made at one hour predicted moisturizing in a two week test for formulations containing glycerin from 0 to 15% concentration. (Li et al J Cosmetic Science, January 2001)
Effect of moisturizers on DPMEffect of moisturizers on DPM(Formulations from ~ 1990)(Formulations from ~ 1990)
Correlation TestGoal determine the correlation between one hour device readings and effects on skin grades in a dry skin test:
One hour Test: 9 subjects
Two week test: 20 subjects
subjects were female, between the ages of 18 and 57 and in good general health with no known skin diseases.
Products contained 0, 5, 10 and 15% Glycerin in identical base
Each subject used each of the 4 products on their legs
DEVICE PREDICTION CAPABILITY: SKICON
ONE-WEEK SKIN SCORE REDUCTION VS ONE-HOUR SKICON MEASUREMENT(CHANGES FROM BASELINE): SKICON PREDICTION CAPABILITY
y = 0.0024x + 0.8118R2 = 0.9681
0.5
0.7
0.9
1.1
1.3
1.5
0 50 100 150 200 250 300 AU
SC
OR
E
Device Regression equation R-square p
NOVA G = 0.0025x + 0.69 0.92 0.04
SKICON G = 0.0024x + 0.81 0.97 0.02
CM 825 G = 0.0209x+ 0.76 0.84 0.08
Regression equations of one week skin grade versus one hour electrical measurements
We do not consider the difference between instruments to be meaningful.
Conclusion
• Single point or short term electrical measurements have been shown to be predictive of long term moisturization for simple formulations using on GlycerinGlycerin as a moisturizer.
F Li, MO Visscher, E Conroy and RR Wickett, J. Cosmet. Sci. 52, 23-33 (2001).
Mechanical Properties of Skin
• There are two fundamental ways to measure the mechanical properties of an object– Apply a known strain and measure the stress– Apply a known stress and measure the strain
• Most skin instruments use the second approach
The Cutometer 575
The Cutometer probe
An optical system is used to measure the height that the skin rises into the probe
The optical system of the Cutometer
Picture courtesy of Courage + Khazaka GmbH
The Cutometer 575 probe
Cutometer curves
Cutometer Parameters
• UE is the elastic deformation of the skin due to the application of stress (vacuum or torque) by the instrument;
• UV is the viscoelastic creep occurring after the elastic deformation;
• UF is the total extensibility of the skin;
• UR is the elastic deformation recovery due to stress removal;
• UA is the total deformation recovery at the end of the stress-off period;
• R is the amount of deformation not recovered by the end of the stress-off period
Cutometer curves
An illustration of the Cutometer curve and analysis (from C+K)
See RR Wickett, Stretching the Skin Surface Cosmetics and Toiletries 116(3), 47-54(2001) for details of Cutometer and DTM analysis
Ratio Parameters
• UA/UF is the overall elasticity of the skin including creep and creep recovery;
UR/UE is the pure elasticity ignoring viscoelastic creep;
• UV/UE is the ratio of viscoelastic to elastic extension called the viscoelastic ratio;
• UR/UF is the ratio of elastic recovery to total
deformation.
Issues with mechanical measurements
• What part of the skin are we measuring?– General principle: to measure the stratum corneum use
the smallest feasible deformation– To measure the dermis use a larger deformation
• Interpretation of data– For moisturization we can look increased Ue and Ur
reflecting increased elasticity.– Many anti-aging treatments claim “firmness” but there
is no engineering definition of firmness
Extensibility of shoulder skin v.
ageCutometer Uf
6 mm diameter probe
Lola Kelly Smalls Ph.D. dissertation University of Cincinnati
Smalls LK, Wickett RR, Visscher M, Effect of Dermal Thickness, Tissue Composition, and Body Site on Skin Biomechanical Properties, Skin Research and Technology, 12 43-49 (2006)
Parameter Pre-treat Post-Treat P-value
NOVA DPM 98.8 116.2 0.001
Ue (200) 0.036 0.048 0.02
Ue (500) 0.068 0.079 0.46
Uv (200) 0.015 0.024 0.07
Uv (500) 0.025 0.029 0.60
Ur (200) 0.026 0.039 0.03
Ur (500) 0.050 0.061 0.26
Effect of vacuum level on Cutometer sensitivity to 1 week of treatment with a moisturizer with limited efficacy
Wickett, RR (2001) Cosmetics and Toiletries 116, 47-54
D’Squames® are an easy way in investigate skin scaling and flaking
They can be graded visually or analyzed by computer
The computer can calculate the Desquamation index (D.I.)
Schatz, et al. J. Soc Cosmet. Chem. 44, 53-63, 1993
6
12..
5
1
n
n nTAID
A = percent area covered by scalesTn = percentage of scale at each thickness leveln = thickness level 1 to 5
We found blacks to have higher visual dryness scores than whites, especially on legs
Warrier(1996) et al J. Soc. Cosmet. Chem. 47, 229-240
D.I. showed the opposite
Warrier(1996) et al J. Soc. Cosmet. Chem. 47, 229-240
The Minolta Chromameter
Color is measured on the L* a* b* scale.
L* = white 0 to 100
a* = red – green 60 to –60
b* = blue – yellow –60 to 60
Using the Chromameter
The color wheel
The color solid
Minolta a* in forearm wash testa* Forearm wash test
0
1
2
3
Bar 1 Bar 2 Bar 3 Bar 4 Bar 5 Water
Bar
a*
RR Wickett, Canadian Chemical News, 49(1), 22-23 (1997).
Correlation between a* and erythema grade in the FCAT
Chromameter L values for various ethnic groups
Alaluf et al (2002) Pigment Cell Res.
Analysis of skin surface textureSilicone replicas are most commonly used
Obtaining a replica from
the peri-orbital
(crows foot) area
Photo courtesy of Ken Marenus
Image analysis can quantify wrinkle depth by the shadow principle
Corcuff et. Al. JSCC 34 177-189 (1983)
Replicas of young and old forearm skin montage
Replicas from the “crows foot” area of the eye
Crow’s foot wrinkle depth versus age
Corcuff et. Al. JSCC 34 177-189 (1983)
Visiometer
• Replicas are died blue
• Light transmission is measured to determine the depth of the lines
Visiometer
Microrelief of the skin determined by the visiometer
Fringe Projection (PRIMOS)
• Phase Shifting Rapid In vivo Measurement of Skin
• Digital micromirror device used to project fringe pattern on the skin surface
• CCD camera records image• Shifting of the fringe patterns by surface
contour allows 3D imaging
Primos measurement on the face
Distortion of fringes by wrinkles
Grey scale coded 3D image
Line profile from the Primos
The VISIA imaging system by Canfield allows for capture of high quality images of the face using different types of light
Image analysis can be performed to pick out hyperpigmented spots and other features of photoaging
Image of face with spots highlighted
Photo courtesy of Greg Hillebrand, used with permission
Moisturizer Testing
• Regression and “mini” regression tests
Regression testing of moisturizers
The ‘Gold Standard’ test of moisturizer efficacy
Three weeks of treatment followed by two weeks of regression
The goal is to separate out the visual effects of the product and show only the real effect on skin physiology
Better moisturizers will be better in the regression phase
Kligman, Cosmetics and Toiletries April 1978 27-35
Rogers et al JAAD 21 714 (1989)
Regression test with Petrolatum
Kligman, Cosmetics and Toiletries April 1978 27-35
Regression test with “Cosmetic” and “Therapeutic” Moisturizers
From Rawlings et al Derm Ther (2004) 17 49-56
The ‘mini’ regression test: One or two week treatment phase, one week to a few days regression. By comparing products on the same panelist and using instruments better sensitivity can be achieved with fewer subjects and a shorter treatment time.
Pretreatment
End of treatment End of Regression
Grove has used 4 day “mini-regression” protocols with grading and conductance measurements on dry legs
• Products applied to 2x2 cm area by trained staff
• Conductance measured with Skicon
• 19 female subjects• Two week washout• Lotions separated in
conductance readings but were not significantly different by skin grade
G. Grove et al poster presentation product names removed used with permission
Rawlings combined visual dryness with Corneometer readings in a 3 day mini regression test
Rawlings et al Derm Ther (2004) 17 49-56
Testing “Ant-Aging” products
Clinical Features of Photo-Aging
• Lines and Wrinkles
• Loss of Elasticity
• Elasticity becomes more anisotropic
• Appearance of “Age Spots”
Methods for evaluation of anti-aging products
• Clinical grading directly on panelists• Grading of high quality clinical photographs• Analysis of replicas• Mechanical measurements• Primos system to analyze wrinkles• VISIA System• Biopsies to evaluate changes in dermal histology
Descriptive grading scale for photoaging
Griffiths et. Al. (1992) Arch Dermatol.;128:347-351
Photographic Grading Scales
• There are several different photographic grading scales
• Griffiths et. Al. (1992) Arch Dermatol.;128:347-351• Larnier et. Al. (1994) Brit. J. Dermatol130. 167-173• Chung (2003)Photodermatol Photoimmunol
Photomed 19: 109–121
The grading scale by Griffiths et. Al. is probably the most commonly used.
The Larnier scale 4 -6
Chung’s scale with Korean subjects
Anti-Aging Studies: General Considerations
• Anti-aging effects take time to demonstrate.• Studies usually run for about 24 weeks and 12 weeks
seems to be a minimum.• Facial studies are usually monadic. That is each
subject tests only one product.• Studies on forearms may be done as paired
comparisons. • Studies must be done double blind.• Vehicle (placebo) Effects can be quite large.
Moisturizing vehicles will produce noticeable effects on fine wrinkles and avoiding sun will improve grades.
A reason for not doing split-face studies on anti-aging products
I’ve been part of a 15 year study on
sunscreens. Every day I put SPF 30 on one side of my body and nothing on the other side
Outline for anti-aging test on facial product
• 60 female subjects with moderate photodamage on the face.
• Randomized or balanced into two groups of 30, active and vehicle or placebo.– Subjects and graders/measurement technicians are blind to the
treatment
– Treatment is to whole face
– Forearms are also treated for biopsies
• Measurements made at baseline and after 3 and 6 months of treatment.
Measurements anti-aging test• Grading.• Clinical photographs or VISIA system.• Cutometer readings on cheek.• Replicas taken from crows foot area of eye for
image analysis or PRIMOS measurements made in eye area.
• Biopsies taken from forearm at baseline and 6 months only for collagen and elastin measurement (this is definitely optional)
Minimum requirements• The test I have described could be called a Cadillac
test as it has a lot of options• At the minimum grading and clinical photographs
should be obtained. • Some studies run for only 3-4 months and
occasionally they are done split face• Pilot studies may be done on photodamage forearms
using both male and female subjects and in this case one arm will get vehicle and the other treatment.
