Eden, G., Tronnier,
H., Heinrich, U.
Testing of sunscreens using improved
Institute for Experimental Dermatology, University Witten/Herdecke, 58455 Witten,
Background and Objective:
in vivo tests of sun protection products an the human skin and in vitro transmission
analyses, a fundamental problem consists of the difference between the skin and
(smooth or roughened) quartz slides and the question of the skin's possible influence
an the sun protection products. The reflectance spectroscopy has the advantage
of being a noninvasive method and thus, of being ethically unquestioned. Measurements
can be easily performed and within short time intervals.
Using a reflectance spectrometer (Multiscan OS20, MBR
Messtechnik) the spectral reflectance of human skin was measured before and alter
application of sunscreen products. Seven sunscreens and one sunscreen base without
UV filters were applied an the volar side of the forearm in an even surface density
of 2 mg/cmZ, since the published SPF is related to this value. The spectral working
range was between 260 470 nm. By means of a novel algorithm developed by us, the
spectral reflectance of the skin treated with the sunscreen base was subtracted,
and the special irradiance of terrestrial sunlight (E) as well as the erythemal
effectiveness (CIE) of skin were multiplied to the absorbance differences. Measurements
were made in vivo and in vitro before and immediately after application, and alter
elapse of additional 30 minutes, 2, 4 and 6 hours after application. Reflectance
spectra were used to determine the SPF for every tested sunscreen product reliant
an the whole UV range.
1. There is a close correlation
between biological and reflectionphotometric determination of the SPF.
An essential biological influence of the sun protection substances during an expected
period of exposure does not occur.
3. The method offers a chance for the
testing of water resistance of sun protection products.
The reflectionphotometric evaluation of sun protection products can
complement in vitro transmission measurements and shows values comparable to biological
The reflectance spectroscopy has the advantage of being
a non invasive method.
Measurements can be easily performed and within short
It provides a very good reproducibility, while taking the
physiologically important parameters into account.
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