HUMAN SKIN UV/VIS REFLECTION SPECTRA 39 DRYING OF SKIN The middle volar forearm of five volunteers (three female, two male mean age = 25 + 4.2a) was dried by means of dry silica gel under occluding polyethylene film for 60 minutes. Before application and after removal of the film, spectra were recorded and normalized. CHANGING BLOODFLOW On the volar forearm of five volunteers, erythema was induced by pressure (dermograph- ism), nicotinic acid benzylester (1% in ethanol), and infrared radiation. Reflectivity was measured before and after applying pressure on the erythematous skin. Venous occlusion was induced by interrupting circulation: two and five minutes later reflection spectra were recorded. INFLUENCE OF A SINGLE TREATMENT WITH SURFACTANTS Tap water (3 ml), soap slurry (10% aqueous dispersion, 3 ml) and SDS (10% aqueous dispersion, 3 ml) were applied for ten minutes on the volar forearms of ten volunteers under a funnel pressed against the skin surface. Before and 1, 10, 20, and 40 minutes after treatment, reflection spectra were recorded. INFLUENCE OF FREQUENT WASHING WITH DETERGENTS Thirty volunteers washed their hands and lower forearms four times per day for two minutes each and for two weeks with a classic soap bar free of perfume and refattening agents. Two, seven, nine, and 14 days after starting treatment, reflection spectra were recorded. RESULTS STANDARDIZATION OF SPECTRA AND IDENTIFICATION OF ENDOGENOUS ABSORBERS The original reflection spectra of BaSO 4 and of skin look similar (Figure 2a). After standardization, the relative spectrum is comparable to formerly published spectra (6) (Figure 2b), with exception of the UV range. It is obvious that reflections are missing (=absorption) in the range of fluorescent NADH (h. max 340-350 nm) in the UVB/ C-range, where aromatic amino acids, especially tryptophan, are emitting fluorecence and around 400 nm, where endogenous and bacterial porphyrins are efficient, fluores- cent absorbers located at special skin sites (nose, upper back). Most of the observed absorption peaks can be related to definite endogenous epidermal or dermal chro- mophores (1). REPRODUCIBILITY The intraindividual variation coefficient determined from ten spectra gained within 15 minutes from the same skin site is approximately 2% from 300-650 nm, showing higher deviations especially in the deep red portion of the spectrum (Figure 3).

40 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 160 140 - 120 100 so 40 20 b 280 320 360 400 440 480 520 560 600 WAVELENGTH [NM] Figure 2a. Original reflection spectra of skin site (a) and of BaSO 4 standard (b). Interindividual variations of untanned lower volar forearms of ten volunteers (date of recording: December) are larger (Figure 4) and wavelength-dependent. A seemingly peculiar phenomenon is the high standard deviation at 320-340 nm (Figure 5), where one of the major absorption bands of NADH is located. The Kolmogoroff-Smirnow test showed that the data at all three selected wavelengths (310, 340, and 480 nm) are distributed in a logarithmic mode. REFLECTION SPECTRA OF DIFFERENT BODY SITES Apparently the most transparent site is the postauricular area (PA), showing intense absorption by hemoglobin (420, 540, 580 nm) in contrast to the palm (Figure 6). The reflectivity of the PA is extremely high in the UV range too, probably on account of its lacking melanin. The palm shows low reflectivity in the UVB and UVA II range and the steepest increase in remittance with rising wavelengths. The reflectivity of the inner upper arm (UA), traditionally considered as a skin site where signs of photoaging are rarely visible, is very high throughout the spectrum from 300-700 nm. The differences between the back of the hand (large lifelong UV dose) and the UA (protected against sunlight) are especially big in the UVA range. Because the date of recording was summer, different levels of pigmentation will strongly influence the data. REFLECTIVITY CHANGES CAUSED BY TAPE AND CYANOACRYLATE STRIPPING The most striking observation is the steadily rising reflectivity in the range of 300-340