Finding the balance

Exposure to ultraviolet (UV) radiation from the sun has been linked to numerous adverse effects on the skin, including premature skin ageing and a significant risk of developing skin cancer. Sunscreen formulations play a key role in mitigating the harmful effects of UV radiation. They are formulated with UV filters that act as protective agents by absorbing, scattering, or reflecting UV rays to prevent them from penetrating the skin, and are divided into two main groups: organic and inorganic filters, each with unique properties and mechanisms of action. However, the regulations and acceptance of these UV filters vary from region to region. 

Some UV filters have faced restrictions due to concerns about their safety or environmental impact. For example, octocrylene (OCR), a commonly used UV filter, has experienced a decline in public acceptance due to emerging concerns, such as potential skin allergies and environmental hazards associated with its use. Compared to 2015, the number of products without OCR increased by more than 400% in Europe.1 This is in line with the overall trend 
that is driving the cosmetics industry: the demand for 
more environmentally-friendly, natural and “clean” beauty products. 

Actively used UV-Filters

Currently, a total of 30 UV filters have been approved and are permitted for use in cosmetic products in the European Union, but only around half are actively used in sunscreen products available in the European market. As regulations tighten, there is increasing pressure on sunscreen for­mulators to develop products that provide high levels of 
UV protection while being safe for humans and the environment. 

Additionally, the demand for multifunctional products grows, meaning that sun protection products are, for example, expected to offer additional skin care benefits.2 Achieving higher levels of protection by increasing the amount of UV filters would lead to more oily products, which would be a downgrade for users from a sensory perspective. Therefore, formulators face the challenge of maintaining product efficacy without compromising on sensory qualities and consumer appeal. 

They must strike the delicate balance between protective and sensory properties, as well as meeting the rising consumer demand for products that are perceived as safe, natural, and environmentally friendly. 

New natural enhancer with 
dual efficacy

To meet this challenge, a new derived-natural ingredient (INCI: Calcium Carbonate, Hydroxyapatite)3 for skin and sun care formulations has been developed that has a dual effect: it enhances the overall formulation aesthetics through homogenous particle shaping, resulting in improved sensory properties, and has also shown to extend UV protection time. 

The functionalised particle (Figure 1) comes in the form of an off-white powder. It is of 100% natural origin content according to ISO 16128 and both COSMOS and NATRUE approved. Additionally, its use makes it possible to reduce the overall UV filter concentration in a formulation and thus helps to improve the ecotoxicological profile of formulations. Although it is not self-absorbing, adding 
the new ingredient to skin and sun care formulations 
allows to enhance UV protection with SPF and UVA via light birefringence. In addition, tests have shown that formulations containing the product are perceived as less sticky and less greasy during application and tend to make skin less shiny.

In vitro performance: absorption

The aim of the evaluation was to investigate how the functional particle could improve the overall UV filter per-
formance without UV absorbing properties on its own. 
To assess the effect of the new ingredient on absorption spectra, a test was performed using a suitable dye. This test evaluates how the presence of the new ingredient affects the sunscreen formulation’s ability to absorb UV radiation at different wavelengths. By measuring the absorption spectra, formulators can gain insight into the UV protection potential and thus optimise the formulation for improved Sun Protection Factor (SPF) and sensory performance.

The effect was studied in a simple model using water-soluble dyes. Patent Blue V was chosen due to its very narrow optical absorption peak (alpha max) at 636 nm4, and a solution c = 6.55 µM of dye concentration was kept constant while the concentration of the new ingredient was varied from 0% to 5% (Figure 2). Thus, when dye molecules are dissolved in the medium, the presence of suspended particles increases the effective pathlength of the light and the probability of absorption by the dyes, resulting in increased dye absorbance.5 For measurements of dye solutions containing the new ingredient, a Perkin Elmer Lambda 20 UV/vis spectrometer with an integration sphere accessory (RSA-PE-20) was employed in order to collect the direct transmitted light and also the light scattered in the forward direction. For absorbance measurements, dispersions were filled into quartz cuvettes (Hellma Analytics), with a thickness of 0.1 cm.

The results showed that the new ingredient has the ability to enhance the performance of dye dissolved in the solution (formulation), via light birefringence. A threefold increase in dye absorbance was observed with the addition of the new ingredient at 3%, and the effective pathlength of the light also increased as shown in Figure 3. 

In vivo and in vitro performance: SPF

To assess the practical performance of sunscreen formulations containing the particle, in vivo and in vitro tests were conducted on the SPF, a numerical measurement that indicates the level of protection a sunscreen provides against the harmful effects of ultraviolet (UV) radiation from the sun. SPF values typically range from low, such as SPF 15, to high, such as SPF 50 or higher. These tests follow globally standardised procedures to ensure that the results are reliable and consistent. By comparing the SPF values of formulations with and without the new ingredient, its effect on the sunscreen’s ability to protect the skin from harmful UV radiation can be assessed. Spectrophotometric methods and in vivo, as well as, in vitro ISO methods were used to evaluate the performance of the formulations with and without the new ingredient in three different countries in parallel, by SPF determination based on ISO 24444 (6) and UVA-PF/CW based on ISO 24443 (7). Several examples of formulations containing different UV filter systems were submitted between November 2021 and May 2022. Especially in formulations combining the new ingredient with organic soluble UV filters (liposoluble and hydrosoluble), the improvement of sun protection performance was confirmed. (Figure 4).

Sensory tests

In a paired comparison test carried out at the ISIPCA laboratory (Paris) with 15 trained panellists, the compared products were applied simultaneously on the forearm and extended over a circle with 4-5cm diameter. For statistical analysis, the highest value for each descriptor was calculated and this value then compared with the theoretical critical value. The tests have shown that formulations containing the new ingredient are perceived as less sticky and less greasy during application. Additionally, they tend 
to make skin less shiny, when evaluated after application of the finished product on the skin, compared with placebo.