Evaluating sunscreen ultraviolet protection using a polychromatic diffuse reflectance device

Blue light protection factor: a method to assess the protective efficacy of cosmetics against blue light-induced skin damage in the Chinese population

BACKGROUND

Previous studies have shown that visible light (VL), especially blue light (BL), could cause significant skin damage. With the emergence of VL protection products, a harmonization of light protection methods has been proposed, but it has not been widely applied in the Chinese population.

OBJECTIVE

Based on this framework, we propose an accurate and simplified method to evaluate the efficacy of BL photoprotection for the Chinese population.

METHODS

All subjects (n = 30) were irradiated daily using a blue LED light for four consecutive days. Each irradiation dose was 3/4 MPPD (minimum persistent pigmentation darkening). The skin pigmentation parameters, including L*, M, and ITA°, were recorded. We proposed the blue light protection factor (BPF) metric based on the skin pigmentation parameters to evaluate the anti-blue light efficacies of different products.

RESULTS

We found that the level of pigmentation rose progressively and linearly as blue light exposure increased. We proposed a metric, BPF, to reflect the anti-blue light efficacy of products based on the linear changes in skin pigment characteristics following daily BL exposure. Moreover, we discovered that the BPF metric could clearly distinguish the anti-blue light efficacies between two products and the control group, suggesting that BPF is an efficient and simple-to-use metric for anti-blue light evaluation.

CONCLUSION

Our study proposed an accurate and simplified method with an easy-to-use metric, BPF, to accurately characterize the anti-blue light efficacies of cosmetic products, providing support for further development of anti-blue light cosmetics.

[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.

Multi-laboratory study of hybrid diffuse reflectance spectroscopy to assess sunscreen SPF and UVA-PFs

BACKGROUND

Proof-of-principle studies have established the use of Hybrid Diffuse Reflectance Spectroscopy (HDRS) methods to assess both Ultraviolet-A Protection Factor (UVA-PF) and Sun Protection Factor (SPF) indices in individual laboratories.

METHODS

Multiple laboratories evaluated 23 emulsions and two spray sunscreen products to evaluate repeatability and accuracy of assessment of SPF and UVA-PF values, using HDRS test systems from various manufacturers using different designs.

RESULTS

All of the laboratories reported similar SPF and UVA-PF values within a narrow range of values to establish the reliability of the HDRS methodology across laboratories, independent of equipment manufacturer or operator.

CONCLUSION

HDRS test methodology provides a reliable objective instrumental estimation of sunscreen SPF and UVA-PF. These data were provided to ISO-TC217 WG7 to substantiate the ongoing development of an ISO Standard HDRS Method.

Noninvasive measurement of the 308 nm LED-based UVB protection factor of sunscreens

The current method for determining the sun protection factor (SPF) requires erythema formation. Noninvasive alternatives have recently been suggested by several groups. Our group previously developed a functional sensor based on diffuse reflectance measurements with one UVB LED, which was previously evaluated on pig ear skin. Here we present the results of a systematic in vivo study using 12 sunscreens on 10 volunteers (skin types [ST] I-III). The relationship of the UVB-LED reflectance of unprotected skin and melanin index was determined for each ST. The spatial variation of the reflectance signal of different positions was analyzed and seems to be mainly influenced by sample inhomogeneity except for high-protection factors (PFs) where signal levels are close to detection noise. Despite the low-signal levels, a correlation of the measured LED-based UVB PF with SPF reference values from test institutes with R² = 0.57 is obtained, suggesting a strong relationship of SPF and LED-based UVB-PF. Measured PFs tend to be lower for increasing skin pigmentation. The sensor design seems to be suitable for investigations where a fast measurement of relative changes of PFs, such as due to inhomogeneous application, bathing and sweating, is of interest.

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

The sun protection factor (SPF) values are currently determined using an invasive procedure, in which the volunteers are irradiated with ultraviolet (UV) light. Non-invasive approaches based on hybrid diffuse reflectance spectroscopy (HDRS) have shown a good correlation with conventional SPF testing. Here, we present a novel compact and adjustable DRS test system. The in vivo measurements were performed using a multi-lambda-LED light source and an 84-channel imaging spectrograph with a fiber optic probe for detection. A transmission spectrum was calculated based on the reflectance measured with sunscreen and the reflectance measured without sunscreen. The preexposure in vitro spectrum was fitted to the in vivo spectrum. Each of the 11 test products was investigated on 10 volunteers. The SPF and UVA-PF values obtained by this new approach were compared with in vivo SPF results determined by certified test institutes. A correlation coefficient R² = 0.86 for SPF, and R² = 0.92 for UVA-PF were calculated. Having examined various approaches to apply the HDRS principle, the method we present was found to produce valid and reproducible results, suggesting that the multi-lambda-LED device is suitable for in-vivo SPF testing based on the HDRS principle as well as for in-vivo UVA-PF measurements.

Evaluating sunscreen ultraviolet protection using a polychromatic diffuse reflectance device

Background

Sun protection factor (SPF) and UVA protection factor (UVA‐PF) are determined using in vivo tests, with high exposures of subjects to ultraviolet (UV) radiation. Hybrid diffuse reflectance spectroscopy (HDRS) enables estimation of both indices using only trace amounts UVB. However, the equipment requires two expensive monochromators that must synchronously scan the spectrum.

Methods

An alternate approach was developed using a polychromatic source that illuminates the skin via a custom light guide array, and the diffuse reflected light is measured with a photomultiplier. The ratio of the diffuse reflectance with and without the sunscreen on the skin determines the polychromatic diffuse reflectance UVA‐PF (PDRS UVA‐PF₀). This factor was used to adjust in vitro UV spectroscopy scans of the sunscreen (with and without UV exposure to assess photostability), to calculate SPF and UVA protection factors. Ten sunscreens were evaluated and compared to in vivo SPF and UVA‐PF values.

Results

The data show an excellent correlation with known in vivo determinations.

Conclusion

This polychromatic HDRS approach uses simpler, faster, and less expensive equipment to determine both UVA‐PF and SPFs without high doses of UV radiation to the test subjects.