Methods for water resistance testing of sun protection products

Water resistance of sun protection products has been found to be best determined by the following methods: (1) Tests for determining UVL filter adherence to merino wool; this gives a rough value for orientation. Values in excess of 6% are suggestive of satisfactory adherence. (2) Tests for determining water resistance of sunscreen products on pig skin constitute a further essential step. Values in excess of 50% provide a realistic basis for tests in humans. In addition to filter adherence the product base, i.e. primarily the emulsifiers, are of special significance. Adequate results can be obtained with both W/O and O/W systems. Tests on volunteers are best done at the time of determining the sun protection factor, i.e. when simulating the events during a 2–3 h sunbath. Simulation should involve a single application of the test product in a pre-defined quantity and all activities conmmonly done in sunlight, e.g. swimming, as well as intermittent exercises to induce sweating. Values are considered as excellent, if 1 MED is not exceeded after 3 h exposure. Sun protection products with this characteristic qualify as adequate ‘all-day’ sunscreen for individuals with average sensitivity. Methodes pour mesurer la résistance à l'eau des produits anti-solaires     

Sun protection factors

The absorption of ultraviolet light by a film of sunscreen product on the surface of the skin is considered from a theoretical standpoint. It is apparent that Beer-Lambert's Law would predict protection factors in excess of the actual factors by many orders of magnitude. The possible reasons for this are discussed in detail, and the relevance of it to in vitro and in vivo measurements of protection factors, and also the in-use situation, are discussed. The implications for formulators of sunscreen products are also discussed.
The methods of measuring protection factors are reviewed. These include instrumental methods, based on both solutions and thin films, model systems, animal methods and human volunteer studies. The current situation with respect to proposed standard methods for measuring sun protection factors, particularly the American FDA method and the German DIN method, is reviewed.     

In vitro assessment of water resistance of sun care products: a reproducible and optimized in vitro test method

The aim of the study was to develop a simple reproducible and reliable in vitro water resistance (WR) method to assess the sun care products. This paper is the result of a scientific collaboration between seven different international industrial laboratories and testing institutes. The same group has already achieved an in vitro protocol for the sun protection factor (SPF) determination [1]. The in vitro WR of sunscreens was tested by applying the same principle as in vivo, which determines the percentage of retention of sunscreen products by assessing the SPF before and after water immersion. Special care was taken to study the parameters influencing the WR and the possibility to follow the kinetics of sunscreen retention during water immersion. The influence of different water qualities has been tested, and osmosed water (1-3 microS cm(-1)) was chosen for the main ring study. Measurement was carried out after 5, 20 and 40 min of immersion. Histograms of selected products demonstrate the percentage of WR at all measuring times and centres, and the regression coefficient to the in vivo determination was shown and statistical calculations clearly demonstrate the reproducibility of the results between the different evaluation centres. The presented method is a practical, convenient and relevant tool for WR screening of sun care and skin care products. It even has the potential to be the starting point for the replacement of the in vivo method in future.     

Evaluation of the prebiotic potential of five kiwifruit cultivars after simulated gastrointestinal digestion and fermentation with human faecal bacteria

We studied the in vitro prebiotic potential of five different cultivars of kiwifruit including the green‐fleshed ‘Hayward’ and ‘Zesh004’ and the gold‐fleshed ‘Hort16A’, ‘Zesy002’ and ‘Zesy003’. The kiwifruit (25 g fresh weight equivalent) were subjected to simulated gastrointestinal digestion before fermentation for 16 h with faecal microbiota from ten individual donors. Microbial metabolites including lactate were quantified while changes in microbiome composition were determined by 16S rRNA sequencing. Lactate concentrations were highest with ‘Hayward’ (P = 0.01) and correlated with the amount of the kiwifruit fibre and polyphenols, chlorogenic acid and cryptochlorogenic acid. All the kiwifruit behaved similar to inulin in increasing the relative abundance of Bifidobacterium (P < 0.001), but unlike inulin, significantly (P < 0.001) increased the abundances of Ruminococcaceae and decreased Bacteroides. In comparison with inulin, the green‐fleshed kiwifruit selectively increased Lachnospira (P = 0.008) while the gold‐fleshed kiwi fruit increased Akkermansia (P < 0.001). These data suggest that the fibre and polyphenol content of the kiwifruit play a role in modulating gut microbial metabolism. Further clinical studies with these kiwifruit cultivars are required to confirm the potential prebiotic benefits that may be achieved by normal dietary intervention.     

A novel ex vivo technique to assess the sand/rub resistance of sunscreen products

A novel ex vivo technique has been used to assess the sand/rub resistance of topical sunscreens. The technique is based on transmission spectrometry using excised human epidermis as the substrate. The sun protection factors (SPFs) of 10 sunscreen products were measured prior to, and after agitation with sand. It was found that the different products retained varying amounts of their photoprotection after agitation, ranging from 40 to 85%. This technique provides a less expensive, less time-consuming and less experimentally problematic alternative to in vivo testing.     

A novel proposal for the assessment of sunscreen product efficacy against UVA

The ideal characteristics are outlined for an assessment method for the protective properties of sunscreen products against UVA. Existing sun protection factors (SPFs) are reliant on largely UVB-induced delayed erythema, which is inappropriate for the UVA. A novel instrumental method for assessing a protection index is detailed which is applicable to the UVA. The validation of the method relies on measurements in the UVB and comparison with conventional SPFs, since no reliable UVA protection index exists. The method uses UV transparent skin casts to which products can be applied. Throughput of appropriately filtered light, with and without applied product, is measured to generate a protection index. Comparison with SPFs confirms that the measurements are similar to those generated by in vivo methods, but that careful choice of the casting medium is essential.     

Comparison of phytochemical profiles,antioxidant and cellular antioxidant activities of seven cultivars of Aloe

A comparative assessment of the phytochemical profiles and antioxidant activities of seven cultivars of Aloe was conducted to evaluate the potential health benefits of Aloe. Aloe arborescens contained the highest levels of phenolic content, total antioxidant capacity by the oxygen radical scavenging capacity assay and cellular antioxidant activity assay. Aloe vera showed the highest levels of flavonoid content and antioxidant capacity by the peroxyl radical scavenging capacity assay. Aloe greenii had the highest CAA value with a PBS wash before adding ABAP. There were no significant differences observed between Aloe arborescens and Aloe greenii. Aloin, aloe‐emodin‐8‐O‐beta‐D‐glucopyranoside, catechin, epicatechin, sinapic acid and chlorogenic acid were identified in Aloe samples by the HPLC analysis. Aloin, aloe‐emodin‐8‐O‐beta‐D‐glucopyranoside and catechin showed strong relationships with antioxidant activity. Significant levels of aloin, aloe‐emodin‐8‐O‐beta‐D‐glucopyranoside and catechin were determined in Aloe greenii, Aloe vera and Aloe saponaria, respectively.     

Etude expérimental de l'indice de protection de produits antisolaires. Valeur prédictive à l'homme

Après avoir rappelé brièvement le spectre d'action biologique du rayonnement ultraviolet du soleil sur la peau normale et les données theoriques de protection qui en découlent, le caractère prévisionnel de différentes méthodes d'étude in vitro et in vivo des antisolaires est commentéà partir de résultats obtenus en laboratoire sur différents principes actifs (PABA, Eusolex 4360, Giv Tan F), et préparations cosmétiques du commerce.
Les méthodes in vitro , basées sur l'absorption dans l'UV des produits, aboutissent à une protection surévaluée et dans ces conditions à une extrapolation trés aléatoire du pouvoir de protection.
La méthode utilisée in vivo (détermination classique d'un indice de protection) souligne, dans le cadre de la prédiction, le choix de la qualité d'absorption du filtre, de la source UV utilisée, mais aussi de nombreux autres facteurs agissant sur la protection. Dans ces conditions, les résultats obtenus chez le cobaye et l'homme avec des irradiations simulant le spectre solaire, montrent alors une concordance satisfaisante pour les principes actifs étudies. Ces observations sont ensuite commentees par comparaison à d'autres travaux publiés faisant mention d'autre source d'irradiation (spectre de raies) et de méthode de détection (thermométrique en particulier).
Predictive nature of laboratory methods in sunscreen studies     

Poly(D,L-lactide) nanoencapsulation to reduce photoinactivation of a sunscreen agent

The use of sunscreens is the 'gold standard' for protecting the skin from ultraviolet light. Octyl methoxycinnamate (OMC) is one of the most widely used UVB filter but it can act as a sensitizer or photoallergen. When exposed to sunlight, OMC can change from the primary trans-form to cis-form and the isomerization, not reversible, conducts to a reduction of the UVB filtering efficiency because the trans-form has a higher extinction coefficient. Photostability is the most important characteristic of effective sunscreens and it can be influenced by formulation ingredients and by applying technological strategies. In this work, photostability experiments, performed on emulsion-gels containing different percentages of OMC free or loaded in poly(D,L-lactide) nanoparticles, were carried out. The presence of a polymeric envelop may act to protect the active ingredient. In this study, the influence of poly(D,L-lactide) matrices on the photochemical stability of the sunscreen agent was investigated. As highlighted in this study, free OMC in different formulations has different photoisomerization degree. Moreover, a dissimilar behaviour was observed by studying different sunscreen concentrations in the same cosmetic formulation. Photostability results show a significant reduction in photoisomerization degree for formulations containing sunscreen loaded in nanoparticles, highlighting that the encapsulation is a suitable strategy to improve OMC photostability. Moreover, sun protection factor (SPF) results show that the UVB filter protective power is also maintained after encapsulation.     

Collaborative development of a sun protection factor test method: a proposed European Standard. COLIPA Task Force 'Sun Protection Measurement', Europe

Standardization of the method to determine sun protection factors (SPF) is fundamental to uniform labelling of SPF values on sun products. The COLIPA Task Force 'Sun Protection Measurement'(SPM), including representatives of major European sun-product manufacturers and contract testing laboratories, was established in 1990 to define methods for sun products testing. The process involved in developing the COLlPA SPF Test Method started with a critical appraisal of previously existing methods, and identification of areas for improvement. Experiments were performed by the participating laboratories to establish the new recommended test protocol which was then confirmed in two multicentred ring tests. Improvements to test methodology included the number and selection of volunteers and skin types, the application of the product, the definition of W output from solar simulators, and the method for assessing erythemal response (MED) including an option to use colorimetry to define objectively the 'erythemal threshold' of skin and to predetermine MED prior to exposure. Four cosmetic formulations and neutral density physical filters (SPF from 4 to 20) were tested in two ring tests. Results showed that variations in SPF of the cosmetic products were, on average, directly proportional to SPF value. An excellent correlation was found between visual and colorimetric SPF assessments (r = 0.99). An acceptable range of values for low and high SPF standard products was also established. The COLIPA SPF test method is now fully defined and supported by experimental data. Its use will harmonize SPF testing throughout Europe and help in the quest for global harmonization in testing sun products.