SUN CARE
Benefits of organic & inorganic UV filters
Bethan Spruce – Croda Europe, UK
As 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 (2015-2017), meaning the need for more sophisticated sun protection products is higher than ever.2
As awareness 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, 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 whilst 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.3 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 the known mildness, lack of skin penetration and other factors such as natural mineral origin and reef-safe claims.
TABLE 1: FORMULATIONS USING EMULSIFIER A Phase A
Ingredients Aqua
Glycerin Xanthan Gum
Magnesium Aluminium Silicate Aqueous TiO2
B
Potassium Cetyl Phosphate C12-15 Alkyl Benzoate
Decyl Isostearate (and) Isostearyl Isostearate
Glyceryl Stearate (and) PEG-100 Stearate Sorbitan Stearate
C
Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine
Ethylhexyl Salicylate D
Butyl Methoxydibenzoylmethane Octocrylene Preservative
www.personalcaremagazine.com Formulators often combine TiO2 TiO2 and ZnO,
due to the different absorbance curves and the good, broadband UV protection when they are used together.4
mostly protects within the
UVB region with limited protection against the UVA region, but this depends 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.5 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. Examples of commonly used types are cinnamates, salicylates and benzophenones. 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.5
Experimental results In vitro SPF evaluation To explore this synergistic effect, six O/W emulsifiers were formulated using two different UV filter systems. The first filter system had organic UV filters only and the second had the same, with the addition of an aqueous TiO2 dispersion. Using this formulation strategy meant it was possible to populate both phases
Organic only Up to 100 3.00 0.20 0.80 –
3.00
10.00 5.00 1.50
1.00 2.00 5.00
2.00 8.00 0.80
Organic + Aqueous TiO2 Up to 100 3.00 0.20 0.80 7.00 3.00
10.00 5.00 1.50
1.00 2.00 5.00
2.00 8.00 0.80
ABSTRACT
With the ever-growing popularity of sunscreens, it is important for the formulator to use the most effective and efficient strategies to maximise the protection potential of each UV filter within a formulation. Studies have shown that exploiting the synergistic effects of a combination of organic and inorganic UV filters can greatly benefit the overall formulation by allowing for higher solids loading, less interaction with organic UV filters and lower costs per unit of SPF. The synergy benefits of using both types of UV filters are well documented and are based upon the different mechanisms of protection from each type of UV filter working differently to each other but also working well together. This has previously been demonstrated in a study using the Monte Carlo calculation, which used typical optical parameters of the skin to characterise the synergy effect when organic and inorganic UV filters are used together. This proved that the synergistic performance is caused by light scattering from inorganic UV filters in combination with organic UV filters.1
of the formulation as the organic UV filters are oil soluble and present in the internal oil phase whereas the aqueous TiO2
dispersion
is present in the external phase. These formulations can be seen below in Tables 1-6. Once formulated, 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 above, the in vitro SPF was measured and compared to 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 Table 7 shows, 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. October 2021 PERSONAL CARE
39
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