Validation of a new in vitro Sun Protection Factor method to include a wide range of sunscreen product emulsion types

Sun-protection factor of zinc-oxide sunscreens: SPFin vitro too low compared to SPFin vivo-a brief review

Sunscreens are mainly characterized by their sun-protection factor (SPF), which is measured according to the in vivo gold standard ISO 24444. Although the SPF concept is simple, SPF values are difficult to measure, due to the rather high variability caused by the complex interaction of light and skin. For half a century, there have been attempts to correlate the costly and ethically controversial in vivo procedure with a non-invasive (in vitro) method. After decades of development, alternative non-invasive SPF methods are expected to become available as ISO standards in early 2025. In particular, sunscreen manufacturers who use zinc oxide (ZnO) in higher concentrations (conc.) (10-25%) in their formulations, are concerned that these new in vitro methods would not confirm the SPF-values on their labels that have been determined in vivo, according to ISO 24444. This brief review reveals that sunscreen formulations with high conc. of ZnO often yield SPFin vitro values that are lower than the SPFin vivo values. This can be explained by the fact that in vitro methods have been developed for conventional emulsions products with organic UV filters, but not for highly concentrated ZnO-alone sunscreens. Fortunately, there seems to be a fix for this problem. There is a difference in density between ordinary emulsions with organic filters (density of the residual oil phase ~ 1.0 g/ml) and highly concentrated ZnO-alone formulations (~ 1.3-1.7 g/ml). As the application of current standards is weight-based, this makes the film on the PMMA plate much thinner, which is likely to lead to lower SPFin vitro values. Preliminary experiments show that using the same volume on the PMMA plates instead of the same weight as organic UV filters gives a much better correlation between in vitro and in vivo SPF results. A recent evaluation of three samples of highly concentrated ZnO sunscreens by the Dutch NVWA seems to confirm these findings. Further experimental evidence is required to fully understand this phenomenon and to adapt the in vitro method for higher conc. ZnO formulations accordingly.

Innovative snail-mucus-extract (SME)-coated nanoparticles exhibit anti-inflammatory and anti-proliferative effects for potential skin cancer prevention and treatment

Nowadays, several studies have highlighted the ability of snail mucus in maintaining healthy skin conditions due to its emollient, regenerative and protective properties. In particular, mucus derived from H. aspersa muller has been reported to have beneficial effects such as antioxidant, antimicrobial activity and wound repair capacity. To enhance antioxidant activity of snail mucus, it was extracted in a hydroalcoholic solution and consequently freeze-dried. The obtained snail mucus extract (SME) was indeed endowed with higher antioxidant activity observed in cell-free models, however it was not possible to test its effects in cellular models as it creates a thick film on the cell surface. Therefore, in order to enhance beneficial effects of snail mucus and extend its potential use, SME was used to develop snail mucus extract-coated gold nanoparticles (AuNPs-SME) which exhibited anti-inflammatory properties on non-tumorigenic cells. LPS-induced inflammation in human NCTC keratinocytes was used as model to investigate the in vitro cytoprotective effects of nanoparticles. Co-treatment with LPS and AuNPs-SME significantly reduced pro-inflammatory cytokine transcription. Moreover, we demonstrated that AuNPs-SME not only can be used for anti-inflammatory treatments, but also as a sunscreen and antioxidant for potential cosmetic applications. Furthermore, AuNPs-SME's ability to selectively inhibit the growth of two human melanoma cell lines without affecting immortalized human keratinocyte viability in the same conditions was assessed. Thus, we demonstrated that snail mucus is suitable for creating innovative formulations and it can be considered a valid candidate for cosmeceutical applications to enrich the snail mucus based anti-age and sunscreen products already present on the market. Moreover, innovative formulations containing snail mucus can be potentially used for the treatment of specific skin neoplasms.

[Characterization of sun protection performance: Quo vadis?]

Die Aufgabe der ersten Sonnenschutzmittel war es, die Entstehung von Sonnenbrand zu verhindern und, dem Zeitgeist der 1950/60er-Jahre folgend, die Bräunung der Haut nicht zu beeinträchtigen. Schnell entstand die Notwendigkeit, die Schutzleistung zu quantifizieren. Ursprünglich unter Zuhilfenahme des natürlichen – heute eines künstlichen – Sonnenlichts wurde eine Methode zur Bestimmung eines Sonnenschutzfaktor (SPF) entwickelt. Dieser ist heute formal als das Verhältnis zwischen minimaler erythemwirksamer UV-Dosis auf mit Sonnenschutzmittel geschützter und minimaler erythemwirksamer UV-Dosis auf ungeschützter Haut definiert (ISO 24444:2019). Drei Beobachtungen stellen die Eignung der Methode infrage: 1) Zwischen-Labor-Variabilität: Trotz strenger Normierung sind Resultate von SPF-Bestimmungen aus verschiedenen Labors und Regionen sehr großen Schwankungen unterworfen. 2) Natürliches vs. künstliches Sonnenlicht: Das Strahlungsspektrum des künstlichen Sonnenlichts unterscheidet sich von dem des natürlichen Sonnenlichts. Die mit künstlichem Sonnenlicht bestimmten SPFs (wie auf allen derzeit im Handel befindlichen Sonnenschutzmitteln abgebildet) sind im Vergleich zur SPF-Bestimmung mit natürlichem Sonnenlicht deutlich zu hoch. 3) Erythembelastung: Bei der Bestimmung des SPF werden die Probanden potenziell schädlicher Strahlung ausgesetzt. Vor diesem Hintergrund werden alternative Methoden – In-vitro-SPF, hybride diffuse Reflexionsspektroskopie (HDRS) und In-silico-Berechnungen – vorgestellt. Diese haben das Potenzial, die heutige mit erheblichen Einschränkungen verbundene Methode abzulösen. Als Sofortmaßnahme wird die Rückbesinnung auf die für alle verständliche Beschreibung niedriger, mittlerer, hoher und sehr hoher Schutz empfohlen, in Zukunft unter Berücksichtigung des Spektrums des natürlichen Sonnenlichtes.

Laboratory testing of sunscreens on the US market finds lower in vitro SPF values than on labels and even less UVA protection

Background

New research has attributed increased significance to the causal link between ultraviolet A (UVA) radiation and immunosuppression and carcinogenesis. In the United States, sunscreens are labeled with only their sun protection factor (SPF) and an imprecise term “broad‐spectrum protection.” Sunscreen marketing and efficacy evaluations continue to be based primarily on skin redness (sunburn) or erythema. We sought to evaluate the ultraviolet (UV) protection offered by common sunscreen products on the US market using laboratory‐measured UV‐absorption testing and comparing with computer‐modeled protection and the labeled SPF values. This approach enables an investigation of the relationship between the labeled SPF and measured UVA protection, a factor that is ignored in current regulations.

Methods

Fifty‐one sunscreen products for sale in the United States with SPF values from 15 to 110 and labeled as providing broad‐spectrum protection were tested using a commercial laboratory. All products were evaluated using the ISO 24443:2012 method for sunscreen effectiveness. The final absorbance spectra were used for analysis of in vitro UV protection.

Results

In vitro SPF values from laboratory‐measured UV absorption and computer modeling were on average just 59 and 42 percent of the labeled SPF. The majority of products provided significantly lower UVA protection with the average unweighted UVA protection factor just 24 percent of the labeled SPF.

Conclusion

Regulations and marketplace forces promote sunscreens that reduce sunburn instead of products that provide better, more broad‐spectrum UV protection. The production and use of products with broad spectrum UV protection should be incentivized, removing the emphasis on sunburn protection and ending testing on people.

The real UVB photoprotective efficacy of vegetable oils: in vitro and in vivo studies

Some vegetable oils are currently being promoted as a safe alternative to commercial sunscreens. The true UVB photoprotective efficacy of 14 virgin vegetable oils and the suitability of the dilution method for determining their SPF value were evaluated. Oils and standard sunscreens were investigated in vitro by the Mansur's method in Slovakia and in vivo by the ISO method in the Czech Republic. SPF values in vitro (0.1; 0.0; 0.4; 0.2 and 0.2) and in vivo (2.5; 1.2; 2.6; 2.6; and 2.8) of the five most promoted oils (from carrot seed, coconut, raspberry seed, rosehip seed, and wheat germ) were significantly lower than the values reported in the controversial studies. We have shown that the overestimated SPF values of these oils were determined by authors who did not strictly follow Mansur's original methodology. The other eight vegetable oils also provide no or negligible SPF values. Only the in vitro SPF value of 11.2 tamanu oil is worth mentioning, probably due to high proportion of calophyllolides. In vitro and in vivo SPF ratios from 1.14 to 0.94 obtained by two methods in two laboratories for six commercial sunscreen oils used as controls confirm the correctness of performing the Mansur's method in this study. However, this dilution method has proven to be fundamentally flawed in determining the SPF value of substances with such negligible photoprotection as most vegetable oils can provide. An SPF value of less than 1, which can be determined by this Mansur's method, is physiologically impossible and meaningless.