Analysis of Human and Porcine Skin in vivo/ex vivo for Penetration of Selected Oils by Confocal Raman Microscopy

Abstract

Background: The subject of oil penetration into the skin is controversially discussed in the scientific literature. Methods: Confocal Raman microscopy was used for analyzing oil penetration into the skin. The following methods were applied in the study: methods based on tracking specific peaks (method 1), the nonrestricted multiple least square fit (method 2), analyzing the lipid-to-keratin peak ratio using the perpendicular drop-down cutoff procedure (method 3), and the Gaussian function-based deconvolution procedure (method 4). Results: The results obtained using methods 1, 2 and 4 show that the investigated oils do not penetrate deeper than 11 µm into human and porcine skin. Petrolatum has a prominent swelling effect on the stratum corneum (32% in vivo, 28% ex vivo), while the other oils exhibit no significant swelling effect. By using method 3, the penetration profile of oils, and especially of petrolatum, into the skin was interpreted incorrectly for various reasons that are addressed herein below. Conclusion: Predominantly remaining in the uppermost corneocyte layers of the stratum corneum, topically applied oils do not reach the viable cells of the stratum spinosum. To exclude any possible mistakes when using the lipid-keratin Raman peak (2,820-3,030 cm^-1), the penetration analysis should be performed using the Gaussian function-based deconvolution procedure.

Radical-Scavenging Activity of a Sunscreen Enriched by Antioxidants Providing Protection in the Whole Solar Spectral Range

“…Ex vivo evaluation of the skin radical formation was carried out on porcine ear skin samples, which is a highly suitable model for human skin [24,25]. Porcine ears were delivered freshly from a local butcher and were used until 2 days later.…”

“…A NIR laser (785 nm, 20 mW on the skin surface, exposure time 5 s) was used to analyze the porcine ear skin samples in the fingerprint region (400-2,000/cm). The utilized CRM was described elsewhere [25] and used for the determination of the penetration depth of topically applied substances into the skin [29,30]. …”

“…To determine the mean penetration depth value of the cream at each measuring point, the cream-treated and untreated skin spectra were compared by the nonrestricted multiple least square fit method using Skin Tools 2.0 software [25] developed by River Diagnostics. With this method it was possible to calculate the depth-dependent coefficients of each individual skin compound (such as cholesterol, ceramide, keratin, urea, water, etc.)…”

“…For the cream-treated skin, an additional coefficient of the cream is also determined and serves as the sunscreen relative concentration in the skin. The nonrestricted multiple least square fit method has previously been described in detail elsewhere [30] and used for the determination of penetration profiles of topically applied substances into the skin [25]. …”

In vivo Raman Microspectroscopy: Intra- and Intersubject Variability of Stratum Corneum Spectral Markers

“…This technique has been applied to study a number of in vivo health-related phenomena in human tissue [1,2,3,4]; it provides a straightforward way to get better insight into the chemical structure and physical behavior of intrinsic molecular components of the stratum corneum (SC) [5,6] and helps to follow up the penetration and action of exogenous molecules [7,8,9,10,11]. …”