Skin Occlusions Measurements Using Condenser TEWL Methods and Capacitance Sensors

H Singh - Faculty of ESBE, London South Bank University, 103 Borough Road, London SE1 0AA, UK
AR Caparnagiu - Kingston University, 53–57 High Street, Surrey KT1 1LQ, UK
P Xiao - Faculty of ESBE, London South Bank University, 103 Borough Road, London SE1 0AA, UK
LI Ciortea - Biox Systems Ltd, 103 Borough Road, London SE1 0AA, UK
EP Berg - Biox Systems Ltd, 103 Borough Road, London SE1 0AA, UK
RE Imhof - Faculty of ESBE, London South Bank University, 103 Borough Road, London SE1 0AA, UK

Introduction
Stratum Corneum (SC) is the outmost skin layer that plays a key role in skin cosmetic properties as well as its barrier functions. Water content and TEWL (trans-epidermal water loss) measurements are two key measurements for the SC characterisation. In this paper, we studied how the SC property varies from skin site to skin site and from person to person, through occlusion measurements by using condenser-chamber TEWL method – AquaFlux [1] and Capacitance sensors [2] and camera photo imaging. Different skin sites are occluded for a fix length of time by using a photo camera lamp glass surface. Fingerprint array sensor, which records the skin hydration images continuously through out the occlusion, and TEWL measurements are performed both before the occlusions and after the occlusions. The results show that different skin sites reacts differently during the occlusions which reflects the different water holding properties and different barrier functions of different skin sites. We have additionally used a photo imaging technique to record the skin images that are being occluded with the camera lamp.


Apparatus
Three skin measurement techniques are used – AquaFlux AF200, Capacitance sensors (MBF200, Fujitsu) and Camera Imaging (SONY DSC-W55 camera with Dermlite II Epiluminescencemicroscopy light lamp) are used to measure in-vivo skin occlusion of different skin sites.

Results and Discussions

All the measurements are performed under normal ambient laboratory conditions, i.e. 20~21°C, and 40~50% relative humidity (RH), volunteers are acclimatised in the laboratory for 20 minutes prior to the measurements. The skin sites used for the measurements are untreated. 

The occlusion measurements is done by first measuring the selected skin site with the AquaFlux, then same skin site is measured using the capacitance sensor. The skin site is then imaged using the photo imaging digital camera. The light lamp of the camera has a glass surface and is in contact with selected skin site. Since the glass surface of the light lamp is in contact with the skin, it is used to occlude the skin and an image is taken every minute for 5 minutes. After 5 minutes of occlusion, the capacitance sensor is used to measure the site and finally the Aquaflux measurement is taken. In total three different skin sites were studied. 

The images from the photo camera are then processed using a dedicated program written in Matlab. The images are separated into their three original colour filters of Red, Green and Blue, then each colours gray-scale values are generated and the average value for all the pixels within an image are calculated. Table 1 shows these occlusion tests result from the photo imaging.

Female Caucasian, 20-30 years								Male Asian, 30-40 years
Volar Forearm								Volar Forearm
	0 min	1 min	2 min	3 min	4 min	5 min			0 min	1 min	2 min	3 min	4 min	5 min
Red	131.423	129.567	130.1743	130.0011	129.2898	129.8782		Red	141.1935	135.937	134.0693	133.094	134.9889	134.99
Green	130.3913	124.7491	125.3285	124.3349	124.4695	123.9983		Green	121.5389	124.2652	124.8552	125.2439	123.8581	123.8552
Blue	131.4757	123.6397	124.7576	124.54	123.9352	124.5205		Blue	109.3358	135.937	114.1685	114.4288	116.16	116.1599
Upper Arm								Upper Arm
	0 min	1 min	2 min	3 min	4 min	5 min			0 min	1 min	2 min	3 min	4 min	5 min
Red	130.2059	127.2306	127.5777	126.1287	125.5655	125.6826		Red	138.2611	135.2307	133.8287	133.5506	133.1282	134.2871
Green	122.2571	123.5045	123.5676	123.5767	124.2271	124.0916		Green	120.3928	122.2922	122.6455	123.2906	122.5278	121.5677
Blue	121.7324	122.6311	122.6886	122.5071	123.1903	123.0019		Blue	101.8515	102.6041	133.8287	101.5861	102.3726	104.4075
Lower Leg								Lower Leg
	0 min	1 min	2 min	3 min	4 min	5 min			0 min	1 min	2 min	3 min	4 min	5 min
Red	128.4427	124.0147	125.2846	125.5396	125.7988	127.2812		Red	143.5055	137.9213	138.9231	140.7148	140.2664	139.5455
Green	122.9635	123.8155	124.0308	123.5781	123.767	125.5539		Green	120.2386	116.6196	117.5008	117.6688	117.4422	117.3345
Blue	122.4448	122.8413	123.083	122.5198	123.2714	125.0113		Blue	99.89186	96.74854	97.58737	98.86824	99.38752	98.99079

Table 1 The average, of different skin sites using  camera measurements.

In general, there is a trend in the photo imaging whereby as the skin is occluded, the  red, green and blue colour gray-scale drops. It is also seen  that  red has the highest gray-scale followed by green and finally blue has the lowest gray-scale. There are some inconsistent reading  that might have been caused by movement of the camera.




Figure 2 shows Table 1’s average values of the three different skin sites of two volunteers. In general all the images have red as the highest values, while green is the second most prominent and blue is at the lowest range. Also it is noted that all skin sites shows a drop in values immediately after the first minute of occlusion.  There are variability of each of the skin sites and especially between the two volunteers.

Shown below are one set of example photos of the Volar Forearm of the female volunteer.  As there is a very subtle change in the luminosity overall image, it’s is more useful to measure the RGB colours for the individual changes.

Using the Aquaflux, a measurement was taken at 0 minutes and at 5 minutes. The table below shows Trans-epidermal Water Loss measurement before and after occlusion of the three  different location of skin.

	Volar Forearm		Upper Arm		Lower Leg
	before	after	before	after	before	after
Female	10.15306	11.1047	11.2664	12.3969	9.17892	11.3531
Male	14.46935	16.7147	12.0438	15.0522	14.9099	20.4585

TEWL measurement shows a consistent increase before and after occlusion and is variable based on the skin site. Similarly the  capacitance sensor shows consistent increase in the gray-scale  after occlusion of the skin site.

The TEWL shows an increase in both volunteers as seen in Figure 4. The reading for the Volar forearm  of both the volunteers increases after occlusion and the male Asian subject has a higher TEWL and higher increase than the female Caucasian subject. This can be seen in all three  skin location of  both the volunteers. The female Caucasian  volunteer  has lower TEWL reading than the male .

Capacitance sensor measurement was taken at  0 minute and 5 minutes  and the results is shown in Table 3 above. In the images, each pixel is represented by an 8 bit grayscale value, 0~255, with 0 represent white (low capacitance) and 255 represent black (high capacitance) [3]. The gray-scale average shown are generally consistent with the TEWL measurement from Figure 4 above. The gray-scale values of the three skin locations drops  after occlusion  as the skin image  has became darker as shown in Figure 5.

	Volar Forearm		Upper Arm		Lower Leg
	before	after	before	after	before	after
Female	140.42	50.16	118.21	33.47	129.39	62.01
Male	156.67	54.68	131.5	65.5	161.98	125.15

Conclusions
The study shows that occlusion measurement of different skin site using the Condenser Chamber Method and the capacitance sensor are producing consistent results. The Aquaflux TEWL measurement are highly sensitive and measuring occlusion of different skin sites using different measurement instruments, we can study the skin site variability and the instrument variability.

The capacitance sensor produces visual images that allows for first hand analysis  We introduced the use of photo imaging in these experiments.The initial study of photo imaging  shows that separation of colour to R,G and B filters suggest that colour red has the highest  concentration in skin images followed by green and blue. Occluding and measuring different skin sites, shows promising results in using capacitance sensor  as an occlusion measurement instrument.

Acknowledgement 
We thank EPSRC and London South Bank University for the financial support.

References
[1] J Fluhr, P Elsner, E Berardesca, H I Maibach, Bioengineering of the Skin-Water and the Stratum Corneum, 2nd Edition, CRC Press, ISBN: 0849314437, (2005).
[2] J Serup, G B. E. Jemec, G L. Grove, Handbook of Non-Invasive Methods and the Skin, Second Edition, ISBN: 0849314372, Informa HealthCare, (2006).
[3]    H Singh, P Xiao, E P Berg and R E Imhof, Skin Capacitance Imaging for Surface Profiles and Dynamic Water Concentration Measurements, ISBS2008.