The measurement and quantification of skin reactions to insults involves certain assumptions about the relation between intensity of color appearance of the skin and the concentration of endogenous chromophores. The underlying assumption is that the Beer-Lambert law is obeyed, i.e., that a linear relation exists between the absorbance and the concentration of each chromophore and that the total absorbance is the linear superposition of the contributions of each chromophore. In this paper the authors compiled the results from a number of interventions on human skin that result in changes in its appearance and small deviations from the homeostatic state, where the results may be accounted for by a single or multiple chromophores. The validity of the assumptions is found to hold for a limited range of responses. The biological constraints need to be considered in certain cases because as we move away from the homeostatic state, complex biological processes are induced.

Background The loss of structural elastin due to intrinsic and extrinsic ageing results in the skin’s inability to stretch and recoil (decrease in elasticity) and manifests as loss of skin firmness and sagging. While other extracellular matrix (ECM) components such as collagen and hyaluronic acid are continually synthesized and assembled through life, elastic fibres are not. Elastic fibre assembly and functionality require fibre cross‐linking, induced by the lysyl oxidase‐like (LOXL) enzymes, which sharply decrease during ageing. Objective To evaluate the enhanced elastogenic effect of a blackberry–dill extract combination, which was hypothesized to induce elastin fibre component synthesis, fibre cross‐linking and reduce elastin fibre degradation. Methods The blackberry and the dill extracts were tested separately and in combination to confirm single ingredient bioactivity and synergistic benefits. Human skin explants, dermal fibroblasts, elastase assays, ELISAs, quantitative real‐time PCRs and spectrofluorometer measurements were used. Moreover, a double‐blinded, placebo‐controlled clinical study was carried out to assess skin elasticity using Cutometer and histologically from biopsies. Results The blackberry extract induced elastin gene expression, elastin promoter activity and inhibited elastic fibre degradation by matrix metalloproteinases (MMPs) 9 and 12. The dill extract induced elastin, collagen and LOXL1 gene expression, resulting in enhanced fibre cross‐linking in human skin explants. Clinically, the blackberry and dill combination treatment displayed synergistic pro‐elasticity activity as compared to each ingredient alone and placebo. Conclusion Taken together, these results demonstrated the two multimodal plant‐based extracts complemented each other in terms of bioactivity and resulted in a synergistic elastogenesis induction.

Abstract. We present a simple and cost-effective optical technique for the simultaneous assessment of pulsating and total blood noninvasively in an inflammatory skin lesion. Acquisitions of diffuse reflectance spectra in the visible range at 6 Hz are used to trace the oscillating components of reflectance. Measurements on erythematous lesions from a UV insult show slow changing signal at about 0.1 Hz and heart-driven regular oscillations at about 1 Hz simultaneously. The results demonstrate the potential of the technique in monitoring both pulsating and steady components of the blood in inflammatory lesions of the skin. C 2010 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3524191] Keywords: skin lesion; blood flow; diffuse reflectance spectra; heart pulsation.Paper 10481LRR received Aug. 29, 2010; revised manuscript received Nov. 11, 2010; accepted for publication Nov. 12, 2010; published online Dec. 23, 2010. There has been heightened interest in noninvasive assessment of blood flow in skin tissues using optical techniques.1 The assessment relies mostly on the use of photoplethysmography 2,3 (PPG) or laser Doppler, using red to near-infrared (NIR) light to probe the dermal vasculature at depths greater than 1 mm and exploiting the pulsatile nature of arterial blood. When a single wavelength is used, a measure of blood flow or perfusion (velocity times concentration of red blood cells) can be obtained from the amplitude of an oscillating signal (ac) that is synchronous to the heart rate or the time-averaged signal that can be associated with total blood volume. Blood oxygenation (SpO 2 ) can be obtained from measurements of plethysmographic pulses at multiple wavelengths based on empirical scaling. The readings of SpO 2 are accurate in a limited range. 4 An accurate assessment of cutaneous microcirculation is still challenging, because probing small volumes of skin with variable content of melanin precludes the use of models based on diffusion approximation to quantify oxy-and deoxyhemoglobin that are pulsating or steady in the same volume of interrogation. In addition, from two independent in-vivo studies for as- sessing UV-induced erythema, different dose-response relations for blood concentration measured from time-averaged diffuse reflectance spectroscopy (DRS) 5 and blood perfusion measured from laser Doppler velocimeters 6 have been found. In this work, we present a simple and cost-effective functional diffuse reflectance spectroscopy (fDRS) system that enables us to study hemodynamics in the papillary dermal vasculature, where the contribution to the signal at the "superficial" vascular plexus is dominant.The configuration of the fDRS system is identical to that of the conventional DRS used in many other studies, 7, 8 except that the spectra are acquired sequentially at 6 Hz. Briefly, one leg of a bifurcated optical fiber probe (600 randomly mixed fibers, 50 μm diameter) was coupled to a Tungstenhalogen lamp (HL2000, Ocean Optics, Dunedin, Florida), and the other leg was cou...

Objective Light therapy has attracted medical interests as a safe, alternative treatment for photo‐ageing and photo‐damaged skin. Recent research suggested the therapeutic activity of red and infrared (IR) lights may be effective at much lower energy levels than those used clinically. This study was to evaluate the efficacy of low‐level red plus near IR light emitting diode (LED) combination on collagen and elastin and ATP production. Methods Human dermal fibroblasts or skin tissues were irradiated daily by red (640 nm) plus near IR (830 nm) LED lights combination at 0.5 mW/cm2 for 10 minutes (0.3 J/cm2). qPCR, ELISAs or histology were used to determine the gene and protein expressions. Fluorescent measurement was used to assess crosslinks of collagen and elastic fibres. ATP production was evaluated by ATP assay. Results Treatment of human fibroblast cell cultures with low‐level red plus near IR lights combination was found to significantly increase LOXL1, ELN and COL1A1 and COL3A1 gene expressions as well as the synthesis of the procollagen type I and elastin proteins. Treating human skin explants with low‐level red plus near IR lights combination similarly induced significant increases in the same gene expressions, type III collagen and elastic fibre formation and crosslinks. ATP production was increased in human dermal fibroblasts after red plus near IR lights combination treatment. Conclusion Low‐level red plus near IR lights combination stimulated the production of collagen and elastin production associated with anti‐ageing benefits. These findings suggest that low‐level red plus near IR LED light combination may provide an effective treatment opportunity for people with photo‐aged skin.

Colorimetry has been used as an objective measure of perceived skin color by human eye to document and score physiological responses of the skin from external insults. CIE color space values (L*, a* and b*) are the most commonly used parameters to correlate visually perceived color attributes such as L* for pigment, a* for erythema, and b* for sallowness of the skin. In this study, we investigated the relation of Lab color scale to the amount of major skin chromophores (oxy-, deoxyhemoglobin and melanin) calculated from diffuse reflectance spectroscopy. Thirty two healthy human subjects with ages from 20 to 70 years old, skin types I-VI, were recruited for the study. DRS and colorimetry measurements were taken from the left and right cheeks, and on the right upper inner arm. The melanin content calculated from 630-700 nm range of DRS measurements was shown to correlate with the lightness of skin (L*) for most skin types. For subjects with medium-to-light complexion, melanin measured at the blue part spectrum and hemoglobin interfered on the relation of lightness of the skin color to the melanin content. The sallowness of the skin that is quantified by the melanin contribution at the blue part spectrum of DRS was found to be related to b* scale. This study demonstrates the importance of documenting skin color by assessing individual skin chromophores with diffuse reflectance spectroscopy, in comparison to colorimetry assessment.

The minimal erythema dose induced by solar-simulated radiation is a useful measure of UV sensitivity of skin. Most skin phototests have been conducted by projecting a flat field of UV radiation onto the skin in an area greater than 15 cm × 15 cm with an increment of radiation doses. In this study, we investigated the responses of human skin to solar-simulated radiation of different field sizes. Twelve human subjects of skin phototype I-IV were exposed to solar-simulated radiation (SSR) on their upper inner arm or on their lower back with a series of doses in increments of 20% in order to determine the threshold dose to induce a minimal perceptible erythema response (MED). Each dose was delivered with a liquid light guide (8 mm diameter on the back or 6 mm on the upper inner arm) and with quartz optical fibers of 200 µm diameter. The resulting skin responses were evaluated visually and investigated with a reflectance confocal microscope and imaging. The erythema response to the microscopic challenge was always diffuse with no clear boundaries extending to several times the exposed site diameter at doses greater than 2 MED. The skin returned to normal appearance from the microscopic challenge after two weeks of exposure while change in appearance for the larger areas persisted for several weeks to months. This new modality of testing provides the possibility to study skin at the microscopic level with a rapid recovery following challenge.

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Erythema and pigment responses of human skin following an acute exposure to ultraviolet radiation (UVR) are frequently used to determine the photosensitivity of the skin. In this study we investigated the responses of the skin to a micro-scale area of UVR exposure (MiR) and compared the responses to a macro-scale area of exposure (MaR). Ten human volunteers were tested with solar-simulated radiation on their upper arm or back using a beam size of 8 mm and 0.2 mm in diameter. The fluence required to produce a minimally perceptible erythema (MED) using the MiR was found to be higher than that for the MaR. The erythema response extended beyond the exposed area and this became pronounced when the beam size was microscopic. Reflectance confocal microscopy in vivo revealed that MiR induced cellular alterations within a confined area of smaller dimensions than the area of exposure. Pigment responses were confined within the areas of cellular damage. The erythema expression of exposed skin recovered faster for the sites receiving MiR even when the applied fluence was higher than the MED for the MaR. Through the use of MiR we were able to visualize spatially dissimilar skin responses of erythema and pigmentation suggesting different cellular mechanisms.