Determination of the protection efficacy and homogeneity of the distribution of sunscreens applied onto skin pre-treated with cosmetic products

Continuous Removal of Single Cell Layers by Tape Stripping the Stratum Corneum - a Histological Study

Studies on the penetration of toxicologically or pharmaceutically relevant substances through the skin and, more specifically, through the stratum corneum (s.c.) often rely on the well-established method of tape stripping. Tape stripping involves the removal of skin layers by means of adhesive tape, which is usually followed by quantification of dermally applied substances in these layers. However, the amount of s.c. removed by each individual tape strip is still a matter of scientific debate. While some studies imply that the amount of s.c. adhering to each tape strip decreases with increasing depth into the s.c., others observed a constant removal rate. All these studies rely on the quantification of the amount of s.c. captured on individual or pooled tape strips. Here, we present an approach whereby we measured the amount of s.c. remaining on excised porcine skin in the process of tape stripping. Staining and bloating of the s.c. allowed to measure its thickness and to count individual s.c. layers, respectively. Histologically, we show that the s.c. remaining on the skin decreased linearly as a function of strips taken. We found that each tape strip removes about 0.4µm of s.c., which corresponds to approximately one cellular layer. With a high coefficient of determination (r²>0.95), we were able to linearly correlate the thickness of the remaining s.c., the number of remaining cell layers and the number of tape strips applied. Furthermore, we elaborate on possible reasons for the discrepancies reported in the scientific literature regarding the amount of s.c. removed by each tape strip.

Layering sunscreen with facial makeup enhances its sun protection factor under real-use conditions

BACKGROUND

The proper application of sunscreen is important to ensure protection of the skin against ultraviolet (UV) damage. Sunscreens are used in various ways in real world situations, which alters their UV protection efficacy. In this study, we simulated typical consumer use of sunscreen, which is often sequentially covered with facial makeup, in a laboratory study.

METHODS

We compared the sun protection factors (SPF) of sunscreen and makeup products after consecutive layering of the products.

RESULTS

The SPF of each sunscreen and makeup product was dramatically lower than stated on the label upon application of a typical amount used by a consumer, which is lower than recommended. For high-SPF products, the drop in effective protection was proportionally greater than those for the low-SPF products upon application of lower doses. However, layering sunscreen and makeup products greatly increased the effective SPF compared with that achieved by single application of each product, even when the amount of each product used was below the recommended level.

CONCLUSION

Layering sunscreen with makeup may compensate for insufficient sunscreen application in real-life conditions by providing an additional source of UV protection and improving the homogeneity of coverage. Our results suggest that recommending consecutive application of sunscreen and makeup products may be a practical and useful approach to improving UV protection that would not require additional steps in the facial care routines of many individuals.