The epidermis is the outermost layer of skin and is composed of cells primarily containing keratin. It consists of about ten layers of living cells (keratinocytes) and ten layers of dead cells (corneocytes). These cells are continually shed from the outside and replaced from the inside in a process called desquamation which is controlled by two biological events – proliferation and differentiation.
One method to non-invasively study biological changes in the skin is using fluorescence excitation spectroscopy. Several characteristic excitation-emission peaks occur in skin that have been related to the epidermal and dermal composition. The magnitude of the peak that occurs at 295nm excitation (F295) has been linked to changes in skin proliferation, cell turnover, epidermal thickening, and skin aging. We hypothesize that changes in this fluorescent signal could be used to assess the potential activity of cosmetic anti-aging compounds to deliver a benefit to skin.
Previous work with retinol and glycolic acid, two commonly used actives that effect epidermal proliferation and exfoliation, has demonstrated an increase in F295 (attributed to tryptophan excitation fluorescence). In this study we present the results of a placebo controlled study that aims to correlate changes in F295 with biological performance (epidermal thickening and Ki67 expression).
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.
The stratum corneum provides a vital physical barrier that protects against external insults and excessive internal water loss. Water activity is thought as a key factor to maintain proper skin barrier integrity via regulating enzyme activities and lipid phase behavior. Consequently, maintenance of an optimal hydration level in SC becomes an important clinical and cosmetic concern.
The objective methods to assess SC hydration are based on either electrical or optical measurements. Electrical techniques used in the current study include high frequency conductance (Skicon), impedance (Nova DPM) and DC I-V curve (Skinsensor). Confocal Raman Microscopy was utilized to document water profile versus depth, and this technique is based on inelastic scattering of monochromatic light from different chemical species of skin.
Water patches were applied on the 14 subjects' forearm for 20 minutes and 1.5 hrs. Skin hydration levels for individuals
were documented by utilizing the mentioned above instruments in vivo. Results show that patterns of water profiles upon the hydration are significantly different among the individuals and these differences may be related to skin barrier function integrity. The intrinsic water content and water absorption upon the hydration were summed corresponding to different depths (3 μm and 15 μm) from the data obtained by confocal Raman microscopy. These results were correlated to the readings from electrical approaches. Superficial (3 μm) but not deeper layer (15 μm) water contents correlated well with the readings from SkinSensor. Neither depth measurements correlate well with the Skicon. There is strong
correlation between the data acquired with Skicon and SkinSensor.
In rhytidectomy the postoperative edema (swelling) and ecchymosis (bruising) can influence the cosmetic results. Evaluation of edema has typically been performed by visual inspection by a trained physician using a fourlevel or, more commonly, a two-level grading(1). Few instruments exist capable of quantitatively assessing edema and ecchymosis in skin. Here we demonstrate that edema and ecchymosis can be objectively quantitated in vivo by a multispectral clinical imaging system (MSCIS). After a feasibility study of induced stasis to the forearms of
volunteers and a benchtop study of an edema model, five subjects undergoing rhytidectomy were recruited for a clinical study and multispectral images were taken approximately at days 0, 1, 3, 6, 8, 10, 15, 22 and 29 (according with the day of their visit). Apparent concentrations of oxy-hemoglobin, deoxy-hemoglobin (ecchymosis), melanin, scattering and water (edema) were calculated for each pixel of a spectral image stack. From the blue channel on
cross-polarized images bilirubin was extracted. These chromophore maps are two-dimensional quantitative representations of the involved skin areas that demonstrated characteristics of the recovery process of the patient after the procedure. We conclude that multispectral imaging can be a valuable noninvasive tool in the study of edema and ecchymosis and can be used to document these chromophores in vivo and determine the efficacy of treatments in a clinical setting.
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