Balancing human and environmental safety

This change is reflected in the number of sun-screens launched without OCR and EHMC, which increased from 15% in 2015 to more than 60% in 2022 in Europe1; 80% of them bearing environmental-related claims. Surely, safety and sustainability map out the future.

Four main pillars for UV-Filters

UV-filters as active ingredients in sunscreens must meet four fundamental requirements: efficacy, registration, safety and freedom-to-operate. Efficacy primarily refers to their ability to absorb UVB and/or UVA light. A filter should be photostable under UV irradiation, not form unknown molecules and be compatible with other UV-filters and cosmetic ingredients. Sunscreens contain a mixture of UV-filters to achieve the desired sun protection factor (SPF) and UVA protection factor (UVA-PF).

Furthermore, water-resistance became an important efficacy factor to maintain the protecting during swimming or sport activities. To achieve the claimed efficacy, the consumer must apply the sunscreen repeatedly (depending on time of exposure) in a certain amount, therefore, a sunscreen should enable a pleasant sensory experience. Even the most efficient sunscreen will be inefficient if the user does not apply it with the right amount; sensory is, therefore, a central aspect linking compliance to provided efficiency. The safety may be reviewed anytime with the disclosure of new scientific data or the publication of new (regulatory) requirements. Finally, the legal aspect offreedom-to-operate not infringing intellectual property of third parties is of prime importance for suppliers as well as sunscreen manufacturers.

same sun, different approaches 

UV-filters must be registered on a positive list before use in sunscreens. Registration comprises a series of tests to demonstrate the safety for human use. UV-filters are registered regionally, with major markets being Europe, USA, Australia, and Japan. This regionally wise registration explains the different number and types of approved filters amongst the regions. For instance, many more UV-filters are approved in Europe than in the USA (figure 1), making it easier to formulate an efficient sunscreen in Europe. 

The regions are also differing in the classification of sunscreens. In Europe, sunscreens are subjected to the cosmetics regulation and classified as cosmetics². The European Comission along with the Scientific Committee on Consumer Safety is responsible for evaluating the 
safety of the molecule before approval and reviewing new data after approval. In comparison, in the USA UV-filters are approved by the Federal Drug Administration (FDA) and sunscreens are accordingly classified as “over the counter” (OTC) drugs.

In both regions, safety aspects are discussed intensively. In Europe, the maximum concentration and/or use conditions of homosalate, benzophenone-3 and OCR were updated recently³. In the USA, the FDA posted in September 2021 a proposed order (substantively similar to 2019 proposed rule) for sunscreens to amend and revise the deemed final order posted in September 2021 for OTC sunscreen products⁴. This proposed order reflects the future requirements for sunscreens. Out of the currently 16 registered UV-filters, only the two inorganic UV-filters titanium dioxide (TiO2) and zinc oxide (ZnO) are proposed as GRASE (Generally Recognised As Safe And Effective). While two additional UV-filters are proposed to not meeting the GRASE criteria, the FDA asked for additional data including Maximal Use Trial (MUsT) studies for the remaining twelve other organic UV-filters to be re-evaluated in light of GRASE. Here, the concerns relate to the lack of data regarding dermal permeation. MUsT studies designed for active drug ingredients are complicated and costly, suggesting that a decision on the fate of the twelve organic filters will last a considerable amount of time.

A question of performance

The penetration of a molecule through the skin depends on properties such as its molecular weight, lipophilicity, presence of functional groups, solubility, and melting point. Filters of newer generation like bis-ethylhexyloxyphenol methoxyphenyl triazine that is not registered in the USA but in other regions around the globe has a high molecular weight and melting point and shows low to no dermal permeation⁵.

By only applying TiO2 and ZnO as UV-filters in the fu-ture in the USA, it will become extremely difficult to meet the high SPF and UVA protection required in the different regions. In Germany, a well-known consumer magazine demonstrated that three out of four sunscreens containing solely inorganic UV-filters did not achieve the claimed SPF⁶.

Given the continuing criticism of established organic UV-filters, only a limited number of UV-filters are considered safe, and this applies to all regions. In Europe, standard filters such as OCR and EHMC have come into disrepute due to their suspicion to be endocrine disruptors and their effect on nature. Moreover, it was found that OCR can release benzophenone over time and with additional exposure to sunlight and heat, which is an additional concern since benzophenone is a carcinogenic substance for animals. Avoiding them in newer sunscreen formulations has been shown to be challenging, particularly in terms of performance achievement⁷.

As an example, figure 1 illustrates the filters that are not under any concern in Europe and USA. It shows that the remaining choice of UV-filters seen as safe is much higher in Europe than in the USA. In Europe, the variety of UVB, UVA and broad-spectrum filters fuel the development of novel, highly effective sunscreens, with different sensorial  properties and formulation formats. Latest effective filters available to European consumers are not accessible to US consumers. 

UV Protection Boosters

Considering the unambiguous future for several UV-filters under concern, sunscreen manufacturers seek for alternatives to boost protection, for instance by by-mixing particles that act by scattering UV light leading to an enhanced efficacy of surrounded UV-filter molecules. Boosters can also be film formers; here they improve the homogeneity of the applied sunscreen layer which enhances protection.

However, some boosters are also molecules with a chemical structure very close to approved filters and might be called “illegal filters” as exemplified by ethylhexyl methoxycrylene (EHMCR) and the approved UV-filter OCR. EHMCR owns the same UV absorbing chromophore as OCR but is not registered as a UV-filter, and has not been assessed in respect of its safety.

The same applies to the booster butyloctyl salicylate (BOS) and the approved UV-filter ethylhexyl salicylate (EHS). These two boosters both exhibit a significant absorption in the UV range. Whereas the FDA requires MUsT studies for OCR and EHS, EHMCR and BOS are currently not on the radar as they are not an approved UV-filter and can be used without in-depth authority controls.

In Europe, the cosmetic directive clearly states that market products cannot use UV-filters other than those listed in annex VI, implying that molecules with inherent UV absorbance not being registered are not allowed⁸. 

Safety plus sustainability

Due to their physical-chemical and environmental properties and in regard of their direct release into the (aquatic)environment, UV-filters are continually and critically discussed by various environmental scientists and regulators. In Europe, the EU chemical agency mainly deals with the safety of chemicals for the environment by the REACH registration and through the CoRAP list which comprises substances that may pose a risk to the environment, and that need further investigation9, such as OCR and EHMC. The potential damages UV filters may have on the ecosystem are discussed widely and a major public concern is related to global coral bleaching. Independently, some authors investigated the impact of UV filters on reef corals, initiating the discussion on the impact of sunscreens on corals. Those study protocols however do show short­comings in study execution and reporting10-14. 

Nonetheless, some governments already took drastic regulatory action on the basis of those studies. For instance, in Hawaii, Bill 135, which prohibits the sale, use or distribution of non-mineral sunscreens (without prescription) and was set effective on 1st October, 202215.

Such regulatory decisions are seen as problematic since sunscreens have been proven to be highly valuable for human health, and organic UV-filters are main contributors to high SPF and high UVA protection. They allow the creation of sensorially appealing sunscreens, clear formulations, or sunscreens without white casts during and after application.

To meet the demand of eco-conscious consumers, some manufacturers are heavily investing in their market sunscreen by developing test protocols to showcase the biodegradability. However, these tests aim to investigate individual substances and not finished formulations16, thus neglecting the fact that even though a formulation may contain readily biodegradable ingredients, it may also contain poorly biodegradable UV-filters. The overall result does not capture the difference in the biodegradability of the various ingredients. Furthermore, considering only biodegradability for environmental safety omits other relevant aspects related to the environment fate and toxicity.

Human and environmental safety

By considering all relevant ecotoxicological parameters, more eco-compliant sunscreen formulations can be developed and a scientific-based tool to assess the environmental impact of UV-filters is needed17-18. The development of new filters must match the safety as well as sustainability requirements.

Going beyond the ecotoxicological aspect of the mere sunscreen formulation, the European Green Deal set the blueprint for a transformational change to improve the well-being of people and protect our natural habitat. It was approved by all Member States committing to turning the EU into the first climate neutral continent. It will have profound implications for the chemical and cosmetics industry in terms of regulation, and rapidly changing consumer preferences. To meet future consumers’ expectations and regulatory requirements, manufacturers’ task is to create sunscreens that effectively combine performance and sustainability while maintaining safety and human health benefits.