Face skin hydration and TEWL

1.1 Skin hydration measurement and comparison of the available equipment

This study consisted of the experiments with the following goals:
1. Compare the accuracy of the instruments in measuring TEWL,
2. Measure the effect of soaking on the skin hydration,
3. Measure the effect of microdermabrasion on the skin hydration and TEWL.
All experiments were performed on the same day at Sinlen Beauty Clinic, London. The room temperature and relative humidity are important reference points for all experiments that involve measuring skin hydration and TEWL. Room temperature was 220C and relative humidity was around 60% at Sinlen Beauty Clinic at the time of the study.
Three participants took part in studies 1 and 3, while study 2 involved four participants. The participants were both females and males, aged 20-30, and they all were healthy, were not on medication and had no long term medical problems. Of the four participants, two had skin type 3 on Fitzpatrick scale, and the other two had skin type 2 and 5.
Experiment 1. Comparing the accuracy of the instruments in measuring TEWL
Method
Choose 6 different normal skin sites (volar forearm, palm, forehead, face, neck, lower leg), use 4 different instruments (Epsilon, Corneometer, Hydrotest Beauty Pro, and Moisture Checker) to measure each site repeatedly (5 times), and calculate the average, and standard deviation.
Results
show the results of five measurements repeatedly on six different sites of three volunteers by using 4 different instruments (3 volunteers).

Forearm
Palm
Forehead

Face
Neck
Lower leg
Figure 5.4. Volunteer No.1
 

Forearm
Palm
Forehead

Face
Neck
Lower leg
Figure 5.5.Volunteer No.2

Forearm
Palm
Forehead

Face
Neck
Lower leg
Figure 5.6.Volunteer No.3
Conclusions: On this pictures we can see that skin pattern, texture and water content is different from site to site. More water content we can see on forehead and neck area, lowest- in lower leg.

Experiment 2. Effect of the skin soaking
Method:
Choose a skin site on left volar forearm, soaking in very wet tissue for 45 min, use 4 different instruments to measure before and after soaking (0, 5, 10, 15, 20, 25, 30 minutes), plot the correction chart between Epsilon and other devices (4 volunteers).
Results
The images below show the skin hydration of total instruments on the same part of 4 volunteers.

Figure 5.7.
 

Figure 5.8.

Figure 5.9.
 

Figure 5.10.

Epsilon pictures for volunteer 1

Baseline T0 T1 T2

T3 T4 T5 T6
Figure 5.11.

Epsilon pictures for volunteer 2

Baseline T0 T1 T2

T3 T4 T5 T6
Figure 5.12.

Epsilon pictures for volunteer 3

Baseline T0 T1 T2

T3 T4 T5 T6
Figure 5.13..

Baseline T0 T1 T2

T3 T4 T5 T6
Figure 5.14. Epsilon pictures for volunteer 4

Results: It’s clearly visible that TEWL and skin hydration is sagnificly increased. Aslo it’s evident that after 15-20 min TEWL and skin hydrtion come back to normal pres- trial results.
Epsilon pictures confirms that just after water soak picture become very bright and whitish. We can see that pistures with a time getting darget as water vaporise to athmosthere. After T3 no noticitble changes in water present and are similar to baseline.
 
1.2 TEWL-based face mapping

Our goal is to analyze
1. distribution of TEWL over the area of the face
2. determine if readings from different areas are statistically significant
3. observe the effect of age on the TEWL distribution

Experiment setup

TEWL measurements were taken with Biox machine AquFlux. The probe determines TWEL by lowering the temperature of skin of a subject over a small area. As such taking measurements also affects nearby areas which makes it practically impossible to use this method for precise face mapping so as to determine the statistically significant borders of areas with specific TWEL.
Because of that we have opted for taking measurements from the following 9 facial points that are sufficiently apart
1. Cheek
2. Chin
3. Eye corner
4. Forehead
5. Lips
6. Neck
7. Nose
8. Under eye
9. Upper lip
There were 23 female subjects in the study, aged between 18 and 70, with the median of 39.5.
In total 501 point-measurements have been taken.
 
Overall sample analysis

Firstly, we analyze the full dataset without splitting it by age.
The table below shows the summary statistics for the TEWL measurements for all points across the subjects. Areas are sorted by the increasing average TEWL.
Area Count Average Standard deviation
1 Neck 27 15.67 10.57
2 Cheek 107 20.36 11.85
3 Eye corner 37 22.88 9.53
4 Forehead 86 26.66 18.28
5 Under eye 72 29.02 13.77
6 Chin 64 32.31 15.45
7 Nose 51 37.43 15.03
8 Upper lip 12 51.77 23.74
9 Lips 45 70.89 22.06
Figure 5.15.
Same information is presented in the chart below, together with plus/minus one standard deviation lines.

Figure 5.16.

Shown on the face, the number show a pattern that appear to reproduce that of the arterial blood flow.

Figure 5.17.
The average values also hint that there may be two clusters on the face in terms of TWEL: upper lip + lips vs the rest.
To make this analysis more quantitative we ran the pairwise Welch test for all points. Results of the test are summarized in the table below, that shows the values of the test’s t-statistic. Paris with the value of the statistic of more than 3 are shown in green.

Welch test Neck Cheek Eye corner Forehead Under eye Chin Nose Upper lip Lips
Neck – 2.01 2.81 3.88 5.13 5.93 7.43 5.05 14.28
Cheek 2.01 – 1.30 2.76 4.36 5.32 7.12 4.52 14.51
Eye corner 2.81 1.30 – 1.50 2.72 3.79 5.54 4.11 13.18
Forehead 3.88 2.76 1.50 – 0.93 2.05 3.73 3.52 11.54
Under eye 5.13 4.36 2.72 0.93 – 1.30 3.16 3.23 11.42
Chin 5.93 5.32 3.79 2.05 1.30 – 1.79 2.73 10.12
Nose 7.43 7.12 5.54 3.73 3.16 1.79 – 2.00 8.57
Upper lip 5.05 4.52 4.11 3.52 3.23 2.73 2.00 – 2.51
Lips 14.28 14.51 13.18 11.54 11.42 10.12 8.57 2.51 –
Figure 5.18.

The table can be summarized as follows. If areas are ordered by average TEWL then
1. Difference in readings from at most third nearest areas (in terms of the ordering) are different from zero with 1% level of significance.
2. The higher the average TWEL is, the more areas the current area is typically different from. E.g. Lips are different from everything.
3. Eye corner is least different from everything else.
4. Lips are most different from everything else.

Age-based clustering
As the next step we cluster the total sample into two groups based on age. The boundary age was selected so as to maximize the Euclidean distance between the vectors of average area TEWLs in clusters, such that number of items per cluster is still representative.
The optimal age turns out to be 35, with the maximum distance of 23.93. Due to low total number of observations, we had to exclude measurements for the upper lip.
The resulting vectors are shown in the chart below. As one can see, in most cases TEWL for the older age group is higher.

Figure 5.19.

The sample statistics and Welch tests for the under 35 age group are presented below.
Area Count Average Standard Deviation
1 Neck 11 19.35 15.01
2 Cheek 22 15.58 6.10
3 Eye corner 8 19.61 6.03
4 Forehead 22 19.46 9.73
5 Under eye 16 24.74 12.17
6 Chin 15 23.11 4.74
7 Nose 15 40.48 18.65
9 Lips 15 61.60 25.26
Figure 5.20.

Figure 5.21.
Welch test
Neck Cheek Eye corner Forehead Under eye Chin Nose Lips
Neck – 0.80 0.05 0.02 0.99 0.80 3.20 5.32
Cheek 0.80 – 1.61 1.58 2.76 4.21 4.99 6.92
Eye corner 0.05 1.61 – 0.05 1.38 1.42 3.96 6.12
Forehead 0.02 1.58 0.05 – 1.43 1.52 4.01 6.16
Under eye 0.99 2.76 1.38 1.43 – 0.49 2.76 5.12
Chin 0.80 4.21 1.42 1.52 0.49 – 3.50 5.80
Nose 3.20 4.99 3.96 4.01 2.76 3.50 – 2.60
Lips 5.32 6.92 6.12 6.16 5.12 5.80 2.60 –
Figure 5.22.
 

One can see that for this age group, face is essentially clustered into 2 areas
• Nose + Lips
• Everything else
The sample statistics and Welch tests for the over 35 age group are presented below. The results are qualitatively similar to those of the overall sample.
Area Count Average Standard deviation
1 Neck 16 13.15 5.16
2 Cheek 85 21.59 12.67
3 Eye corner 29 23.79 10.18
4 Forehead 64 29.14 19.87
5 Under eye 56 30.25 14.05
6 Chin 49 35.12 16.50
7 Nose 35 36.22 13.53
9 Lips 30 75.53 19.06
Figure 5.23.

Figure 5.24.

Welch test Neck Cheek Eye corner Forehead Under eye Chin Nose Lips
Neck – 4.48 4.65 5.71 7.51 8.18 8.79 16.81
Cheek 4.48 – 0.94 2.66 3.72 4.96 5.48 14.42
Eye corner 4.65 0.94 – 1.71 2.42 3.75 4.19 13.06
Forehead 5.71 2.66 1.71 – 0.36 1.75 2.10 10.85
Under eye 7.51 3.72 2.42 0.36 – 1.62 2.02 11.45
Chin 8.18 4.96 3.75 1.75 1.62 – 0.33 9.61
Nose 8.79 5.48 4.19 2.10 2.02 0.33 – 9.44
Lips 16.81 14.42 13.06 10.85 11.45 9.61 9.44 –

Figure 5.25.
The key specific observation from the Welch test for this age group is that Lips and Neck are significantly different from everything else.
The overall conclusions are
1. Lips are consistently different from almost everything else, independently from the age group
2. For under 35 age group, lips are however indistinguishable from nose
3. For over 35 age group, neck as different from everything else as lips

 
1.3 Hydration-based face mapping

Our goal is to
1. analyze the distribution of water content over the area of the face
2. determine if readings from different areas are statistically significant

Experiment setup
Hydration measurements were taken with Epsilon machine.
We have opted for taking measurements from the following 8 facial points that are sufficiently apart
1. Cheek
2. Chin
3. Eye corner
4. Forehead
5. Lips
6. Neck
7. Nose
8. Under eye
In total 1174 point-measurements have been taken.
1.3.1 Overall sample analysis

The table below shows the summary statistics for the hydration measurements for all points across the subjects. Areas are sorted by the increasing average hydration.
Area Count Average Standard deviation
1 Lip 86 21.42 5.75
2 Nose 116 23.13 4.65
3 Forehead 232 24.05 6.40
4 Chin 157 25.28 6.99
5 Neck 108 26.15 8.19
6 Cheek 239 26.46 7.36
7 Eye Corner 92 27.32 7.89
8 Under-eye 144 28.00 7.93
Figure 5.26.
Same information is presented in the chart below, together with plus/minus one standard deviation lines.

Figure 5.27.
The main difference from the TEWL measurements is that there is no clear clustering. The whole face is hydrated fairly uniformly, except, perhaps, lips. Lower hydration of lips seems to be related to the lips having the largest TEWL.Shown on the face, the corresponding path differs significantly from that of TEWL.
• The ordering of the Lip/Nose/Forehead path is reversed.
• The “central” vs “peripheral” segments are reversed.

Figure 5.28.

To make this analysis more quantitative we ran the pairwise Welch test for all points. Results of the test are summarized in the table below, that shows the values of the test’s t-statistic. Paris with the value of the statistic of more than 3 are shown in green.
Welch test Lip Nose Forehead Chin Neck Cheek Eye Corner Under eye
Lip – 2.26 3.51 4.64 4.72 6.46 5.73 7.26
Nose 2.26 – 1.53 3.06 3.37 5.19 4.52 6.17
Forehead 3.51 1.53 – 1.77 2.36 3.81 3.55 5.05
Chin 4.64 3.06 1.77 – 0.90 1.61 2.05 3.14
Neck 4.72 3.37 2.36 0.90 – 0.34 1.03 1.80
Cheek 6.46 5.19 3.81 1.61 0.34 – 0.90 1.89
Eye Corner 5.73 4.52 3.55 2.05 1.03 0.90 – 0.64
Under eye 7.26 6.17 5.05 3.14 1.80 1.89 0.64 –

Figure 5.29.
The table can be summarized as follows. If areas are ordered by average TEWL then
1. Difference in readings from at most third nearest areas (in terms of the ordering) are different from zero with 1% level of significance.
2. The pattern is fairly uniform, there are no outliers.
3. It is quite striking how different are nose and under eye.

Below are several examples of hydration visual face maps, obtained using Epsilon from people of different sexes, ages and ethnicity. One can clearly observe significant differnece among the members of the sample group.

Female, Caucasian, 41 Figure 5.30.

Female, Caucasian, 52 Figure 5.31

Female, Caucasian, 53 Figure 5.32

Female, Caucasian, 33 Figure 5.33

Male, Asian, 38 Figure 5.34
 
1.4 Before and after physical exercise TEWL analysis

Here we present results of the effects of the physical exercise on TEWL. The measurements were taken foe one male and for one female.
The main observation that only for forehead one can notice a considerable change, both for the male and for the female.

Female Before After
Cheek 17.59 19.74
Chin 34.77 46.88
Forehead 22.98 69.91
Lips 67.57 66.40
Nose 37.44 40.46
Under Eye 24.43 27.92
Figure 5.35

Figure 5.36
 
In addition to that, male’s TEWL readings for the cheek also showed considerable difference before and after the exercise.

Male Before After
Cheek 30.01 62.70
Chin 19.69 34.19
Forehead 20.58 91.91
Figure 5.37

Figure 5.39

 

1.4.1 Forearm

In this case pretty much both measurements and standard deviations show similar patterns for each explanatory variable. The data suggests that there is variance with age and white ethnicity is definitely different from black.

Water content

Standard deviation
 
1.4.2 Back of hand

In this case, age still produces most variance, only now just under 20s’ group is different from the other two, which are similar between themselves. Standard deviations for Asian ethnicity are also appreciably different from those of the black ethnicity.

Water content

Standard deviation
 
1.4.3 Palm

On this area changes in both measurement and standard deviations with age are most dramatic, with under 20’s age group clearly standing out. In terms of ethnicity, measurement and standard deviations for the for whites are somewhat different from those for the blacks. Sex is still irrelevant.

Water content

Standard deviation

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