Electrohydrodynamic spray applicator for homogenous application and reduced overspray of sunscreen

Abstract

Background The recommended amount of sunscreen by hand application (2 mg/cm2) is in reality not achieved, which decreases the homogeneity and thereby the effective sun protection factor (SPF). Materials and Methods The homogeneity of sunscreen applied by a newly developed spray applicator using an electrostatically charged aerosol, for which a hand rubbing of the formulation is not necessary, is evaluated. In vivo experiments were performed on the volar forearms of human volunteers using the spray applicator compared to the standardized hand application according to ISO 24444. Results The distribution homogeneity was assessed qualitatively using in vivo laser scanning microscopy and quantitatively by absorption spectroscopy after tape stripping and by the standard deviation of multiple spatially displaced reflectance measurements for non‐invasive SPF determination below the minimal erythemal dose, which showed a significantly higher homogeneity by 20.9% after spray application compared to hand application. Conclusion Non‐invasive SPF determination of multiple spatially displaced reflectance measurements was proven to be a suitable method for the non‐invasive determination of the sunscreen distribution homogeneity. Electrostatically charged spray application increased the sunscreen distribution homogeneity on the skin and can reduce the amount of overspray.

Noninvasive measurement of the 308nm LED‐basedUVBprotection factor of sunscreens

“…The reflectance values of high and very high LED‐based UVB‐PFs are however close to or below the noise limit (0.1 units). One can conclude that comparison of sunscreen distributions by this method requires the comparison of sunscreens with a similar SPFs as shown by Schleusener et al [ 26 ]…”

“…The point‐by‐point measurement of skin reflectance using the described sensor potentially allows to measure the homogeneity of UV reflectance and thus sunscreen distribution at a spatial resolution of about 5 mm. [ 26 ] Our results show that the point‐by‐point variation of the reflectance increases with increasing LED‐based UVB‐PF. The reflectance values of high and very high LED‐based UVB‐PFs are however close to or below the noise limit (0.1 units).…”

In vivo sun protection factor and UVA protection factor determination using (hybrid) diffuse reflectance spectroscopy and a multi‐lambda‐LED light source

“…Now the multi‐lambda‐LED light source with 8 LEDs covering the whole UV range allows more spectrally resolved and thus accurate measurements. These could be beneficial for testing the reproducibility of SPF values, for example, to determine the sweat‐resistance or homogeneity of a sunscreen product [7, 27]. Furthermore, the in vivo spectra may be useful for research purposes, since skin filter interactions are measured in the UVA and in the UVB range.…”

“…Beside seeking shade and wearing protective clothing, applying sunscreen products is an important strategy of photoprotection [3]. The efficacy of a sunscreen product is dependent on the type and amount of UV‐filters [4], the vehicle of the product [5, 6], as well as its quality to create a continuous film over the surface of the skin [7]. Commercial sunscreen formulations are constantly being adapted to the state of research and customized to target susceptible groups like children or dermatological patients.…”