Fun in the Sun – the Safe Way

Group interview with:
BASF, Sun Protection Facilitator GmbH and Symrise

Sunscreen products, containing UV-filters, are used worldwide to protect from the negative effects of sunlight. However, in order to provide this photoprotective function, sun screen products need to be photostable and be retained by the skin.

How do you make your UV/UVA filters photostable? 

Marcel Schnyder, Head of Global Technical Center Sun Care, BASF: 

The photostability of a sunscreen is predominantly linked to the photostability of the individual UV filters and their combination used in a sunscreen. The most efficient way to achieve a photostable sunscreen is by the selection of UV filters with inherent photostability. In case UV filters with a limited photostability are used (i.e., Avobenzone / BMDBM), they need to be stabilized to avoid degradation of the UV filter function under irradiation. Some UV filters are used that can also act as a stabilizer (typically Octocrylene or BEMT). In contrast the use of stabilizers which have an inherent UV absorbing function, but are not registered as UV filters, is critical as the safety assessment for UV filters is more comprehensive than for other cosmetic ingredients. 

Uli Osterwalder, Owner and Principal, Sun Protection Facilitator GmbH:

Some UV filters are inherently photostable, so we do not have to worry about them. The best-known example of a photolabile UV Filter is Avobenzone (ButylMethoxy diBenzoyl Methane, BMBM). Formulators do know how to stabilize it in sunscreens. In the future, for a UV Filter not to be completely photostable could prove to be beneficial. From an environmental impact point of view, BMBM is found in lower quantities in the sea, compared to other UV Filters although it is used more often in sunscreens. This is an indication and almost a proof that photo instability in beneficial.   

Ev Suess, Vice President Business Unit Sun Protection, Functionals & Colors and Marek Busch, Project Manager Business Unit Sun Protection, Functionals & Colors, Symrise:

Most of our UV filters are photostable in themselves and don’t need stabilization. We stabilize the UV filter Avobenzone (Neo Heliopan® 357), which is not photostable per se, by combination with other UV filters such as Octocrylene (Neo Heliopan® 303) and Bemotrizinol (Neo Heliopan® BMT) or, alternatively, with our emollient Corapan® TQ (Diethylhexyl2,6-Naphthalate) which also protects Avobenzone from degradation.

In addition, the final UV filter combinations must always be tested for photostability.

What are your testing methods for photostability?

Marcel Schnyder: The ISO method 24443 to evaluate the UVA Protection Factor (UVA-PF) of a sunscreen includes an irradiation step and indirectly include the photostability requirement. A photoinstable sunscreen would therefore not meet the European Commission (EC) recommendation for UVA protection because it would degrade significantly during irradiation.

In addition, there are alternative methods where a defined film of a sunscreen is irradiated by a defined UV dose, and the remaining UV filter amount is detected by using High Performance Liquid Chromatography (HPLC). 

Uli Osterwalder: If the conventional SPF-method ISO 24444 is used to test the performance, photostability is inherently tested with it. Not sufficiently photo-stabilized formulations would lead to an inferior SPF.  To consider photostability, the emerging alternative test methods which are all non-invasive contain an extra irradiation step on a PMMA plate that is mimicking skin, similar to the UVA-PF method ISO 24443. Hence, photostability is an integral part of SPF and UVA-PF testing. For research purposes photostability can be tested by analyzing the remaining UV filter content of a sunscreen by analytical methods, e.g. HPLC.

Ev Suess and Marek Busch: We formulate the UV filters individually with a realistic maximum usage concentration in a basic sunscreen formulation and apply it at 1.3mg/cm² (according to Colipa guidelines 2011 and based on ISO 24443:2021) on PMMA plates with a defined roughness. 

After 30 minutes of drying time in the dark, the absorption of the sunscreens in the UVA and UVB range is measured. Subsequently, at an irradiance of 10 MED, the absorption of the sunscreen is measured again. 

The ratio between the absorption before and after irradiation gives the photostability of the sunscreen formulation, which may contain single or combinations of UV filters.

To demonstrate a photostabilizing effect in, which we saw in the absorbance curve, the same formulation is applied to PMMA plates and tested via HPLC. Samples for irradiation and non-irradiation are prepared and washed in a solvent suitable for HPLC evaluation. Finally, the HPLC measurement shows us that the photoinstable UV filter is protected, when the same or a similar concentration of the molecule is found both in the samples before and after irradiation.

How do you test a sunscreen’s protection factor?

Marcel Schnyder: The sun protection factor is measured in vivo on 10 human subjects (ISO 24444). The endpoint of measurement is the erythema of the individual subjects. The SPF claim indicates the length of self-protection time for an individual without them getting sunburnt. For example, an SPF of 30 protects a person with fair skin and self-protection time of 10 minutes (without sunscreen) for up to 300 minutes (5 hours). However, the measurement is done with an application rate of 2 mg/cm². Compared to these standard conditions, in real world applications, the application amount is in the area of only 1 mg/cm². This means the real protection is reduced by around 50%. In addition, it has to be taken into account that the application of a sunscreen is never homogeneous and there are areas with lower protection where sunburn can thus occur. Moreover, mechanical treatment, sweat or water exposure remove some of the sunscreen and reduce its protection. Due to all these factors, the recommendation is to use a sunscreen with a higher SPF (SPF 30-50+) depending on the self-protection time (the darker the skin tone, the longer the self-protection time). In addition, the sunscreen should be reapplied regularly and especially after contact with water. 

Uli Osterwalder: The various SPF testing methods all have their merit. It depends what phase of development a sunscreen is in. Before thinking about going to the laboratory, ideas and concepts of sunscreens can already be tested in-silico. BASF and DSM-Firmenich provide reliable SPF simulation tools on their respective websites. To improve an existing sunscreen formulation, an in-vitro transmission method may be used for relative assessment of the improvement. There is now also a non-invasive in-vivo method available. The hybrid method HDRS measures the UVA part in-vivo and extrapolates into the UVB part by attaching in-vitro results. Finally, once a sunscreen is fully developed, a conventional in-vivo test according to ISO 24444 is still advisable. 

Ev Suess and Marek Busch: Before determining a sun protection factor for a sunscreen formulation, the following three steps must be followed:

  1. Calculation of the sun protection factor.
    Since UV filters differ in their absorption efficacy when compared at the same concentration, we calculate a specific SPF value for each percentage of UV filter. In this way, we obtain an initial estimate.
  2. In-vitro SPF
    In this method, UV transmittance is measured through a thin film of a sunscreen sample applied to a roughened substrate before and after exposure to a controlled dose of radiation. This is another indication of the SPF.
  3. In-vivo SPF
    In a final step, we verify our formulation in an in-vivo study based on the determination of sun protection by hybrid diffuse reflectance spectroscopy, a non-invasive method as it does not induce an erythematous skin response from UV irradiation. This method has been extensively tested to correlate with the ISO 24444:2019 standard for the measurement of sun protection factors and provides us with a SPF based on screening.

In the area of sunscreens, regulations can vary widely, affecting both formulation and measurement of sunscreens. We measure formulations developed specifically for North America according to FDA monograph standard 21CFR201.327, which includes UVA protection requirements. While the European Union requires a UVA protection factor that is at least 1/3 of the stated SPF, the FDA requires a critical wavelength of at least 370 nm to indicate broad spectrum protection.

In the media, we read of concerns about the potential toxicity of sunscreens to marine and freshwater aquatic organisms such as coral, as well as the concern about nano particles. How do you address these issues and educate consumers?

Marcel Schnyder: The human and environmental safety of sunscreens is tested prior to approval. Registered UV filters are seen as safe and efficient for human life and the environment. However, the eco toxicological and human toxicological data sets are different for the individual UV filters. Currently, we see a trend toward UV filters based on conventional chemistry being formulated out from sunscreens due to their ecotoxicological and / or human toxicological data sets. The efficacy of UV-filters is adding to this trend, as there are newer
UV filter molecules with higher efficiencies. In older sunscreens, formulations required more than 30% UV filter composition to reach an SPF 50, but with more efficient UV filters, this can be reduced to 10-15% leading to less environmental impact at identical performance. 

BASF established a new methodology especially developed for sun protection products – evaluating the environmental compatibility of UV filter systems in sunscreens. The methodology supports the transparent assessment of UV filters based on internationally recognized criteria and comprises eight different parameters, from biodegradation and aquatic toxicity to endocrine disruption potential. It not only considers environmental factors for individual UV filters but provides a comprehensive environmental evaluation of filter systems. This open access tool is called EcoSun Pass. 

Uli Osterwalder: Yes, the discussion about the environmental impact of sunscreens, in particular their UV filters started in 2008 and again in 2015, which resulted in the ban of some UV filters on some Pacific Islands, including Hawaii. In recent years, claims like “reef-safe” also became popular in Europe. In my view this issue should be handled scientifically, similar to human safety. Because it has not been a big issue until recently, the authorities, e.g. ECHA in Helsinki have not yet concluded their studies. In the meantime, UV filter suppliers did step in and provide help with their scientific assessment, e.g. BASF with their EcoSun Pass and DSM-Firmenich with their Ecoprofiling, which is built into their Sunscreen-Optimizer.   

Regarding concerns about nano-particles, my opinion is very simple: Nano means BIG, i.e. there should be no concern (see next question on human safety). 

Ev Suess and Marek Busch: To address these concerns, we need to consider a few points:

  1. The entire formulation should be evaluated, as UV filters are not individually released to the water when consumers go swimming in open waters.
  2. Where is your sunscreen actually being released into the environment? If you wear your daily sunscreen and end up washing it off at home, the sunscreen will be washed down the drain and end up in the sewer system where the water gets cleaned, cleared and treated. In these occasions the sunscreen is not directly released in open waters.
  3. Testing of the effects of UV filters on marine and freshwater organisms is still being evaluated to have validated and agreed upon test methods, while previous studies often showed a lack of methodology.
  4. While we want to keep aquatic ecosystems intact, there is a serious risk of skin cancer from too much UV radiation from the sun because it damages the DNA in our skin cells. To protect your skin and minimize the impact on marine life, we recommend using a sunscreen that has been tested to be very water resistant and letting it dry for at least 20 minutes after application to allow a protective film to form, making it more resistant when you go swimming in open waters.

Mineral sunscreen vs. chemical sunscreen: which is safer? This has been an issue for some time. What is your opinion?

Marcel Schnyder: Mineral (inorganic) as well as organic UV filters which are listed on the positive list of the EC Cosmetic Directive can be used and are safe for use in sunscreens. The regulation also informs about the maximum concentration that can be used. The list of approved UV filters is constantly being monitored and updated by the EU commission in relation to the latest findings in regard of environmental and human safety. 

Therefore, both organic and inorganic sunscreens are safe for the end consumer, however differences exist with respect to their efficiency. Organic molecules are designed to achieve the highest possible performance and photostability, and therefore the UV filter amount needed for high performance is less in the case of organic UV filters. In addition, inorganic UV filters are neither soluble in oil nor in water and are therefore used as particles. This results in a white painting effect which needs special measures to be reduced e.g., by manufacturing nano particle size.

For sunscreens with light texture and low/no white painting effect, organic UV filters are preferred.

Uli Osterwalder: Now we talk about human safety. The distinction mineral vs chemical sunscreen is misleading, e.g. Titanium Dioxide and Zinc Oxide are of course also chemicals, as well as are their coatings. I prefer the distinction Particulate UV filters vs Soluble UV filters. BTW the term Sunscreen refers to the final product in the American understanding. Generally, when a UV filter is approved by an authority, e.g. the EU Commission or the US FDA, it is by definition safe. If this were not the case we would all expect the authority to remove such an unsafe UV filter from the positive list. In the US there are currently only TiO2 and ZnO on the category I list (GRAS/E, generally recognized as safe and effective), all other filters in use are on the category III list (more safety data required), but they can be used for the time being. 

However, one may or even should assess the potential risk of using sunscreens, especially if one belongs to a potentially vulnerable group (children, pregnant woman, breastfeeding mothers...). The major concern is skin permeation and the resulting bioavailability of organic, soluble UV filters. The inorganic, particulate UV filters, mostly in Nano form do not permeate into the skin, and are thus considered inherently safe (except for the potential airborne route via lungs; therefore, the restrictions in sprays). So, my recommendation: if you want absolutely no foreign UV filters in your body, look out for the (Nano) declaration and make sure that there are no other organic (soluble) UV filters in the INCI list.

Ev Suess and Marek Busch: Regarding the safety of UV filters to humans when applied topically to the skin, the European Commission’s Scientific Committee on Consumer Safety (SCCS) evaluates safety based on available scientific data and recommends maximum concentrations for each UV filter. There is only anecdotal evidence that mineral sunscreens are less likely to cause skin reactions, which is why they are preferred for sensitive skin. However, sunscreens containing chemical UV filters can also be formulated for sensitive skin, as shown by tolerance tests of the final products. In addition, any cosmetic product, including sunscreens, entering the cosmetics market (whether in Europe, the U.S. or other regions) must be safe, as manufacturers must ensure that products undergo scientific safety evaluation by experts before they are sold.

What country-specific features are there to consider in the production of sunscreens?

Marcel Schnyder: Each region has its own registration status of UV filters. In the US, sunscreens are considered as Over the Counter (OTC) drugs, while in Europe, sunscreens fall under the cosmetic regulation. In the EU, new and improved molecules are registered and approved by the authorities, while in the USA, the FDA has not approved any new UV filters in the last 20 years. Authorities in Asia and LATAM mainly follow the EU registration, with some adaptations. Due to the main differences of approved UV filters in the EU and the USA, it is not possible to have one formulation that suits the end consumer globally.

Uli Osterwalder: I have already mentioned that there is difference between the US and the rest of the world, when it comes to sunscreen. For sunscreens to go on the US market, they have to be produced according to Pharma standards (GMP). Each region may also have a bit a different positive list for the UV filters. Making a global sunscreen, thus means that the formulation has to meet the lowest common denominator. As you can imagine, such a sunscreen may then be available everywhere, but it will less likely be the best in the world. 

Ev Suess and Marek Busch: In general, lists of approved UV filters differ by region, but also in terms of the maximum allowable concentration for the same UV filter. This may vary by region depending on formulation type, as aerosol products sometimes have special restrictions on allowable UV filter concentrations.

The declaration of nano pigments is required in the European Union if the average diameter is below 100 nm, which is not provided for in the FDA guidelines. This declaration applies to insoluble UV filters and is placed in brackets: [NANO]

When testing water resistance in the EU, sunscreens can be tested as water resistant or very water resistant. For the first statement, the sunscreens must develop at least half of their protective properties based on the sun protection factor after two immersions in water for 20 minutes each time. In order for a sunscreen to be described as very water-resistant, it must have at least half the original sun protection factor after four 20-minute exposures. This is in contrast to the method used for sunscreens in the United States, where the FDA can only report the SPF for water-resistant sunscreens, which is measured after immersion in water.

Finally, the way the UVA protective properties of sunscreens are measured differs between the EU and the US. For the EU and as an international standard ISO 24443:2021, the assessment of an in-vitro UVA protection factor is acceptable, while the FDA requires the measurement of a critical wavelength that defines at which point the range below the absorption curve reaches 90%. The higher the critical wavelength, the more the absorption curve covers the UVA spectrum.

Pocture Cretits: Max Topchii, AdobeStock

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