The sunscreen: a complex evaluation

Evaluating the performance of sun protection products is a complex task considering in-silico, in-vitro, in-vivo or hybrid methods. The criteria that have the most influence on the performance of these products include the composition, repartition, photostability, absorbance, and distribution of inorganic and organic filters, as well as the galenic properties of the product (spray, compact powder, oil, cream, etc.). In addition, the performance of sun care products is also impacted by other factors such as wrinkles, skin locations, sweat, hair, application procedures and quantity.

To ensure the accuracy and reproducibility of in vitro and in vivo testing, it is essential to implement systematic control testing such as BIPEA inter laboratory comparison tests and audit of the global process such as Suncert diagnostics and FEBEA audit. Additionally, the gap between standardised application and real-life conditions of use should be thoroughly investigated, including anti-salt, anti-sweat, and anti-sand claim substantiation. Among all the available methods, the in-vitro SPF is strongly required by the industry and governmental organizations delivering results equivalent to the in-vivo SPF according to ISO 24444 method. As evidence, the degree of protection should be measured using standardized, reproducible testing methods and take photo-degradation into account as recommended by the European Commission.

From an ethical standpoint, the use of erythema to assess UVB exposure may not be a viable long-term solution due to the potential skin damage it can cause. Fortunately, the Hybrid Diffuse Reflectance Spectroscopy (HDRS) method and in-vitro method offer promising alternatives that should be available soon.

Are the various damages that UVB, UVA, Blue Light, Infrared may cause to the skin a target for new claim substantiation? Beyond anti-sun spectrum objectivation, and index determination, can we evaluate complementary photo ageing performances such as antioxidants, anti-free radicals, anti-ageing, anti-dark spots…?

Nowadays, there are different sunscreen testing procedures for claiming the Sun Protection Factor: (SPF), UVA Protection Factor (UVAPF), Critical Wavelength (CW), Water Resistance (WR)… Fortunately, mainly according to ISO (International Organization for Standardization), standards are available to harmonize these methods worldwide.

For many years, the Sun Protection Factor (SPF) has been evaluated on the skin of human volunteers in vivo. The current in vivo SPF test method used in Europe (ISO24444:2019) was created by a team of international experts in the International Standards process and is widely used to support labelled protection claims or in-market control.

Up to now, the SPF value given on the bottle of each sun protection product must be determined by the generation of sunburns at the back of at least 10 volunteers. This is not only invasive but also time consuming since volunteers must come back after 24h for evaluation of the minimal erythemal dose.

The European Commission has been a strong advocate for the development of alternatives to the current gold-standard in vivo SPF test method (ISO24444:2019). It is therefore essential that any alternative method can demonstrate a high statistical correlation with the current gold standard in vivo SPF test method (ISO24444:2019). Unfortunately, predicting in vivo SPF test results using alternative methods has been a difficult scientific endeavour. Several alternative methods are in various stages of development, and five methods are currently undergoing statistical characterisation vs the gold standard ISO24444:2019 method in a multi-stakeholder technical consortium (ALT-SPF1).

Two of those methods have ring-study data evaluating their correlation with ISO24444:2019. Results of these methods have been published in peer-reviewed journals and both are formal work items in the final stages of standardisation in the ISO/TC217/WG7 ‘Sun Protection Test Methods’ Working group.

These two methods are expected to be the first alternative SPF methods to be published as full ISO standards, as early as 2025 (whereupon they will be preferred reference alternative methods, as stated in the European Commission Recommendation of 2006).

UV filters can lead to a partial or complete loss of their effectiveness or even to a possible transformation into a hazard substance and undesirable by-products. Laboratories work to anticipate physical and chemical degradation of raw materials based on photodegradation and new criteria (chemical and toxicological) to ensure the safety of sun care products. However, it has been demonstrated that some skin reactions due to photoallergic contact are caused by using many commonly organic sunscreens. In this context, the maximum content of UV filter in products has been limited in cosmetics by the European Commission (Annex VI-1223/2009). Different instrumental techniques are used to analyse the UV filters: NMR spectroscopy, Raman spectroscopy, gas chromatography/mass spectrometry, high-performance liquid chromatography/UV detector.

Consumers are increasingly challenging the photoprotection of cosmetics brands, particularly in terms of in situ conditions such as real conditions of use on the beach. There is currently no standardized in-vivo or in-vitro method for assessing Sand Resistance. To address this issue, a new in-vitro method has been developed by HelioScreen to allow the evaluation of the Sand Resistance percentage of a sunscreen product by comparing the in vitro SPF before and after a specific agitation in a standardized sand.

For the coloured sunscreen products, the limits remain at %BL ≥ 35% and BL-CW ≥ 385 nm. The criteria for Blue Light protection claims should be adjusted for uncoloured products. The HelioScreen approach suggests that for uncoloured sunscreen products, the minimum requirements should be %BL ≥ 30% and BL-CW ≥ 385 nm to make a valid Blue Light protection claim.

Solar radiations penetrate the skin, and their energy is absorbed by constitutive molecules, with consecutive damages like oxidation and inflammation. Evolution brought effective defences such as pigmentation to quench radiations, anti-oxidation, and clearance processes. However, an excess of sun exposure disrupts those self-defences, leading to uncontrolled reactive oxygen species (ROS) production, DNA damages, proinflammatory response and microbial dysbiosis. Many of these mechanisms can be evaluated with controlled radiations on 3D skin models studying various biological markers and cell signalling pathways.

The Hawaiian archipelago has seen the gradual disappearance of corals and its marine life caused by the pollution of certain chemical compounds present in sunscreens. January 1, 2021, Hawaii prohibited the over-the-counter sale of sunscreen products containing oxybenzone and octinoxate, chemical compounds considered particularly “dangerous” to the balance of the underwater environment. A recent review of environmental contamination and potential health impacts on aquatic life from the active chemicals in sunscreen formulations published in March 2022 in the Australian Journal of Chemistry by Nial J. Wheate said that the level of sunscreen chemicals found in samples varies considerably between regions, time of year (higher in summer months), and time of day.

This publication confirms that from numerous studies, it is known that the active chemicals in sunscreens can have potential hormonal/oestrogenic activity and non-hormonal effects, including acting as teratogens, altering gene regulation, inducing changes in antioxidant and free radical production, and inducing coral bleaching.

This article precises that when damage does occur to reefs and animal life, there are often other causes that are more likely impacting the aquatic life including changes in water temperature, water turbidity, elevated nutrient levels, and the presence of pesticides and medicines used for human and animal health.

Zebrafish are featured in most of the ecotoxicology studies and are well recognized as a standardized model for this type of study. The Zebrafish areeasy and cheap to grow and share some genetic, physiological, and anatomical similarities with mammals. They are routinely used to study the effect of chemicals on vertebrate embryonic development. As they have transparent bodies the direct visualization of the organ development is easy. To evaluate the endocrinian activity, translucent embryos are used as an in-vitro test to measure thyroid activity of an ingredient or a formula.

Moreover, for the Marin Ecotoxicity, there is an ISO norm (16712) that enables the study of the acute toxicity on Amphipods, Corophium Arenarium, determining the acute toxicity of marine or estuarine sediments to amphipods. Marine or estuarine amphipods which typically live below the sediment surface are exposed to contaminated sediment. The endpoint for this test is the mortality percent. The salinity and temperature vary on the species of amphipod used.

On the Preclinical Testing Platform of Skinobs, cosmeticians and evaluation experts can retrieve, for free, 16 specifics in-vitro tests provided by 30 CROs around the world. Other specific photo-aging effects can be found by selecting specific claims. Then, for the in-vivo UV SPF and UVA-PF, there are 28 methods available and connected with more than 76 CROs in the Clinical Testing Platform.

To sum up, harmonizing test methods between and within laboratories ensures that all solar products are of the highest quality. The beauty and dermocosmetics industries can look forward to worldwide industries and regulatory authorities unifying reference methods and labelling rules. This will ensure that human health (e.g., nano, and endocrine disruptors) and the environment (ecotoxicity testing, coral protection) are respected, while still allowing for the development of high-performance sun protection products with the additional features consumers.