UV Transmission Assessment: Influence of Temperature on Substrate Surface

Jul 1, 2013 | Contact Author | By: Sébastien Miksa, Dominique Lutz and Céline Guy; HelioScreen Labs, Creil, France
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Title: UV Transmission Assessment: Influence of Temperature on Substrate Surface
temperaturex in vitro SPFx critical wavelengthx sunscreen productsx
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Keywords: temperature | in vitro SPF | critical wavelength | sunscreen products

Abstract: This work evaluates the impact of temperature on test substrate surfaces during the application, spreading and drying steps of the in vitro method to measure ultraviolet (UV) transmission. The authors work in a range of temperatures, between 20°C to 35°C, and demonstrate that controlling temperature is a key parameter and should be strictly controlled to ensure reliability.

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S Miksa, D Lutz and C Guy, UV transmission assessment: Influence of temperature on substrate surface, Cosm & Toil 128(7) (Jul 2013)

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Editor’s note: This article is the first in a series of three considering the effects of certain test variables on SPF results. Here, the authors assess how variations in substrate surface temperature affect SPF. The next, to appear in September 2013, evaluates SPF results based on different substrates. The third will focus on the influence of pressure on SPF and is scheduled to appear in November 2013.

During outdoor recreation, protection against photo damage can be afforded by sunscreen products, which act by absorbing or scattering ultraviolet (UV) radiation. Historically, evaluating the level of protection afforded by sunscreen products against UVB, i.e., the 290–320 nm solar spectrum range, is based on an in vivo method and universally expressed by its SPF. This method involves comparing the UV radiation dose required for the appearance of a biological endpoint, erythema, with and without protection. And although UVB radiation is mainly responsible for sunburn, recent studies have shown that UVA radiation (320-400 nm) can cause a number of detrimental effects in human skin. Until now, the in vivo method used for evaluating protection against UVA has been based on Persistent Pigment Darkening (PPD). However, in both cases, for ethical, economical and practical reasons, companies and health authorities want to substitute these in vivo methods with in vitro methods.

The determination of in vitro SPF by means of a spectrophotometer was initially described by Diffey and Robson, then modified and improved in view to evaluate the skin protection against UVB brought by a product. This method is based on the assessment of UV transmittance through a thin film of sunscreen sample spread onto a roughened substrate. Concerning in vitro UVA Protection Factor (UVA-PF) and critical wavelength (CW) evaluation, much work has been conducted in recent years to establish a reliable method. Similar to Diffey and Robson, the Cosmetics Europe, formerly COLIPA, and International Organization for Standardization (ISO) in vitro methods are based on an assessment of the UV transmittance of a thin film of sunscreen sample spread on a roughened substrate after exposure to a controlled dose of UV radiation from a defined UV source.

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Figure 1. Temperature control device and metallic support

Figure 1. Temperature control device and metallic support

This support is designed for use with a specific polymethyl methacrylate (PMMA) substrate.

Figure 2. Monitoring of the temperature with and without metallic support during whole process

Figure 2. Monitoring of the temperature with and without metallic support during whole process

Variations in temperature of the substrate surface were monitored over several minutes during the whole process of application, spreading and drying steps.

Figure 3. Protocol with and without metallic support

Figure 3. Protocol with and without metallic support

Protocol with and without metallic support during the whole process

Figure 4. Percentage of product

Figure 4. Percentage of product

Percentage of product depending on temperature according behavior

Figure 5. In vitro SPF for two products

Figure 5. In vitro SPF for two products

In vitro SPF for two products thermo-sensitive according temperatures

Figure 6. Spearman’s correlation results

Figure 6. Spearman’s correlation results

Spearman’s correlation results between temperatures and in vitro SPF

Figure 7. In vitro SPF decreases with temperature elevation

Figure 7. In vitro SPF decreases with temperature elevation

By means of results of difference calculation method (see Table 3) and correlation (see Figure 6), the influence of temperature only on in vitro SPF is presented here.

Figure 8. In vitro SPF identical with temperature elevation

Figure 8. In vitro SPF identical with temperature elevation

By means of results of difference calculation method (see Table 3) and correlation (see Figure 6), the influence of temperature only on in vitro SPF is presented here.

Figure 9. In vitro SPF increases with temperature elevation

Figure 9. In vitro SPF increases with temperature elevation

By means of results of difference calculation method (see Table 3) and correlation (see Figure 6), the influence of temperature only on in vitro SPF is presented here.

Footnotes [Lutz 128(7)]

a The Heliotemperatura temperature control device is manufactured by HelioScreen Labs.

b The Helioplate HD6 PMMA plates are manufactured by HelioScreen Labs.

c The Altisurf 500 lab workstation is manufactured by Altimet.

d The Labsphere UV-2000S transmittance analyzer is manufactured by Labsphere Inc.

e Ultraviolet Transmittance Analyzer Performance Validation Standards are distributed by Labsphere Inc.

f Helioplate HD0 PMMA plates are manufactured by HelioScreen Labs.

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