WHITE PAPER SUN CARE
Inorganic UV filters are often referred to as physical UV filters due to their mode of skin protection. The most used inorganic UV filters are titanium dioxide
(TiO2
) and zinc oxide (ZnO), which are growing in popularity due to their known mildness and lack of skin penetration, as well as other factors such as natural mineral origin and reef-safe claims. Formulators often combine TiO2
and ZnO due to the
different absorbance curves and the good broadband UV protection when used together. TiO2
mostly protects within the UVB region with limited protection against the UVA region. However, this is dependent on the particle size.
In contrast, ZnO has an absorbance range within both the UVB and UVA regions meaning they are usually combined to reach broad spectrum protection.
Organic UV filters are commonly referred to as chemical UV filters due to their mode of skin protection, which is different to that of inorganic UV filters. Organic UV filters are usually aromatic compounds with a carbonyl group and examples of commonly used types are cinnamates, salicylates and benzophenones.
White paper
A WINNING COMBINATION
Croda’s Bethan Spruce explains the synergistic benefits of using organic and inorganic UV filters in sun care
A
s awareness of the harmful effects of UV light increases, the need for effective sun protection products becomes a necessity. At present, in the UK alone, there are approximately 16,200 new melanoma skin cancer cases every year (2015-17) meaning the need for more sophisticated sun protection products is higher than ever.
As awareness also increases around the importance of SPF and UVA ratings, this means that sun protection products need to follow current trends, meet strict guidelines in terms of high SPF and UVA protection and meet sensorial requirements. For the formulator, lots of factors must be taken into consideration. They not only face strict regulations to abide by, which are different in each region, but the products must pass strict and expensive in vivo SPF and UVAPF tests while also taking into account the ethical and environmental implications of each product, all whilst keeping the sensory and the cost of the product desirable.
This is where taking advantage of the synergistic effects of using a combination of organic and inorganic UV filters can help within a formulation.
22 December 2020
In contrast to inorganic UV filters, usually a cocktail of organic UV filters is necessary within a formulation to achieve broad spectrum protection as they typically have narrow absorbance ranges.
EXPERIMENTAL RESULTS In vitro SPF evaluation To explore this synergistic effect, six oil in water emulsifiers were formulated using two different UV filter systems: the first filter system being organic UV filters only and then the second filter system being with the same organic UV filters but with the addition of an aqueous TiO2
dispersion.
Using this formulation strategy meant it was possible to populate both phases of the formulation as the organic UV filters are oil soluble and present in the internal oil phase whereas the aqueous TiO2 external phase.
dispersion is present in the
Once created, these formulations underwent in vitro SPF testing to assess the differences in SPF between the UV filter systems and the in silico predicted SPF values. For the 12 formulations with the six different emulsifier systems and two different UV filter systems, the in vitro SPF was measured and compared with the expected in silico SPF values. To measure the in vitro SPF, automated spreading was carried out using the HD-Spreadmaster (HelioScreen) onto two types of PMMA plates (HD6 and SB6) at 25°C regulated using the HD-Thermaster (HelioScreen) and then measured using the UV2000S Labsphere. As you can see in table 1, the in vitro SPF values were consistently much higher in the formulations that used the combination of both organic UV filters and an aqueous TiO2
dispersion.
Figure 1 also shows the in vitro results of the 12 formulations with and without aqueous TiO2
dispersion
along with the expected theoretical values. As can be seen in figure 1, the in vitro results for all the systems with aqueous TiO2
has much higher in vitro SPF
results than were predicted and thus could be representing the synergistic effect between the two types of UV filters.
cosmeticsbusiness.com
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