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| New Developments in
Skin Barrier Measurements |
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R.E. Imhof , M.E.P. De Jesus, P. Xiao, L.I. Ciortea and E.P.
Berg.
Skin Moisturization,
2nd edition, Editors: A.V. Rawlings & J.J. Leyden, in press.
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| Summary:-
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| 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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