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Tape Stripping Method in Humans: Comparison of Evaporimetric Methods
By: Hongbo Zhai, MD, and Howard I. Maibach, MD, University of California School of Medicine
Posted: January 30, 2009, from the February 2009 issue of Cosmetics & Toiletries.
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Ventilated chamber (open chamber) is capable of continuous TEWL measurement. Unventilated chamber (closed chamber) method might be incapable of continuous TEWL measurement and might tend to occlude the skin.10 However, both methods might be interfered with by the microclimate near the surface of the skin, thereby influencing the water loss to varying extents. Extensive descriptions of methods and measuring principles of TEWL and devices can be found elsewhere.10,11,13
The current study compared the sensitivity between an open and a closed chamber device by utilizing the tape stripping method. Both devices yielded TEWL values that were similar on stripped human skin in vivo. This was in accordance with the authors’ previous report on healthy intact skin.9 If the occlusion time of the closed chamber device on the skin is too long, saturation might occur. If this closed chamber device is left on skin for only 10 sec or so, saturation does not occur.
Many factors might influence the stripped SC amounts.6-8 Therefore, the authors also determined the SC protein amounts in the removed strips to ascertain if other factors such as contact area and pressure of two devices on skin might affect the tape stripping amounts. However, there was no statistically significant difference of SC stripped amounts between two sites measured by open versus closed chamber devices.
To perform accurate and reliable measurements, several factors and sources of variation need be taken into account.10,11,14,15 One limitation of the study was that few individuals were observed, so it is possible that TEWL measurements, although high, could be further elevated. Another issue is that no factory calibration was made immediately prior to this preliminary study; hence the inter-instrument and intra-instrument variation might be affected.
These limitations suggest the need for a validation study with more measurements covering the whole range of TEWL before drawing any conclusion on the similarity and differences between the methods. Thus, the authors are not making the general conclusion that the differences in the data here are explained by the differences in the measuring principles of the two devices. Limited results of TEWL values measured by both instruments were consistent with small standard deviations, suggesting that both might be used in stripped human skin in vivo and other clinical situations as well. A recent experiment validated both instruments.16