New Developments in Skin Barrier Measurements
RE Imhof, MEP De Jesus, P Xiao, LI Ciortea and EP. Berg.
Skin Moisturization, (Editors: AV Rawlings & JJ Leyden). 2nd Edition, pp466-82, Informa Healthcare 2009.
Print ISBN: 9781420070941, eBook ISBN: 9781420070958.
The skin barrier is fundamental to our existence, protecting us from dehydration and xenobiotics. Different techniques of skin barrier assessment are used, depending on whether the measurements are carried out in-vivo or in-vitro. For in-vivo skin barrier assessment, the main technique is transepidermal water loss (TEWL) measurement, because it is safe and non-invasive. Of course, TEWL measurements only give information about the water barrier, whereas other chemicals will generally have different penetration properties. For in-vitro barrier assessment, there are more methods available. This is because chemicals and formulations other than water can be used irrespective of toxicity, and because there is access to both sides of the barrier membrane. TEWL measurement may also have a role in this case because of the need, according to OECD guidelines, to verify the integrity of the membranes prior to the their use in penetration measurements. Tritiated water, electrical resistance and TEWL procedures are recognised for such tests.
In this chapter we focus on barrier measurements using TEWL methods, because this is where significant new developments have recently come to market. At the heart of these is the introduction of closed-chamber TEWL technologies, which are having significant impact in both in-vivo and in-vitro applications. The established open-chamber technology is known to suffer from a number of limitations, including vulnerability to disturbance from ambient air movements, calibration inconsistencies, angular dependence, temperature dependence and contact pressure dependence. Chief of these is disturbance by external air movements and this was the main motivation behind the developments of newer closed-chamber instruments.
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