SUN CARE 0.1g initial 3% Silica (4) 0.1g post 3% Silica (4)
69
Figure 1: Comparison of sunscreen appearance on skin, without and with boosting powder
It is also hypothesized that the powder distribution (either in the oil phase or at the interface) can be affected by the order of addition. A more homogeneous powder distribution will enhance boosting ability, which is why we see discrepancies between the same use levels but with different processing methods. It is recommended when formulating with a booster to test which use level and processing is optimized for that specific formula and also consider capabilities in scale-up and manufacturing. Opacity testing was conducted as a proof
of principle test, therefore only the ‘post-add’ series of formulas were tested. While opacity measurements did show some numerical differences between the different formulations (Table 5), no discernible difference was seen upon application (Figure 1).
Zinc oxide sunscreen base A smaller number of powders were evaluated in the zinc oxide sunscreen system. The level of zinc oxide (20%) was chosen to give an in vitro SPF of approximately 26 (reported as 25, in accordance with FDA Proposed Order 000008)2
. In vitro results and opacity results are shown
in Table 6. Only the in-process method was used in the preparation of these samples. Comparing the opacity values of this
system (Table 6) with the opacity values in the mixed mineral filter system (Table 5), we can see that the use of zinc oxide only does give lower opacity values (which would lead to less whitening on skin) as compared to the use of both zinc oxide and titanium dioxide. Through the use of boosting powders, it is still possible to achieve high in vitro SPF without the
25% ZnO
20% ZnO+ Calcium Sodium Borosilicate
25% ZnO
TABLE 6: IN VITRO SPF RESULTS AND OPACITY RESULTS, ZINC OXIDE UV FILTER SYSTEM Booster INCI
In vitro SPF 1% No booster
Calcium Sodium Borosilicate Microcrystalline Cellulose (1) Microcrystalline Cellulose (2)
Microcrystalline Cellulose (and) Cellulose Gum
Oryza Sativa (Rice) Starch (and) Oryza Sativa (Rice) Bran Wax Silica (2) Silica (6)
60+ 40 30 40 40 30 25
25 25
60+ 40 30 40 30 30
TABLE 7: IN VITRO SPF AND OPACITY RESULTS, ZINC OXIDE UV FILTER SYSTEM Sunscreen formulation
Base system (no booster, 20% ZnO)
Base system + 1% Calcium Sodium Borosilicate Base system + 3% Microcrystalline Cellulose (1) Base system (no booster, 25% ZnO)
use of titanium dioxide. As an SPF value of 60+ is achievable by using
20% zinc oxide and a boosting powder, it was of interest to see how the opacity would compare to an SPF 60+ formulation using zinc oxide as the only UV filter, but without the aid of a boosting powder.
Those results are shown in Table 7. The results
show that an SPF of 60+ is achievable, with a similar or lower opacity, while reducing the zinc oxide content. A comparison of appearance on skin for a
sunscreen with 25% zinc oxide (no booster), and a sunscreen with 20% zinc oxide and 1% Calcium Sodium Borosilicate is shown in Figure 2.
20% ZnO+ Calcium Sodium Borosilicate
SPF 26
60+ 60+ 60+
21.1 17.8 19.9 15.7 19.1 17.5 17.5
3% 1% 11.9
19.5 15.6 14.3 14.4
20.0 16.4 21.5
Opacity 3%
Opacity 12.4 21.1
15.6 23.6
Conclusion As demand for mineral based sunscreen formulations continues to rise, formulators are searching for techniques to innovate and increase aesthetic appeal to the consumer. One way this can be achieved is with the help of boosting powders in the formulation.
The addition of boosting powders to a
zinc oxide-based sunscreen system was shown to help achieve the desired SPF with less UV filter, thereby decreasing opacity on the skin and creating a more desirable formulation for the consumer.
References 1. Labsphere. UV-2000S Ultraviolet Transmittance Analyzer. 2022. https://
www.labsphere.com/wp-content/ uploads/2022/06/UV-2000S.pdf
0.1g initial application 0.1g post application
Figure 1: Comparison of appearance on skin for a sunscreen with 25% zinc oxide (no booster), and a sunscreen with 20% zinc oxide and 1% Calcium Sodium Borosilicate
www.personalcaremagazine.com
2. US Food And Drug Administration. Proposed Order (OTC000008): Amending Over-The-Counter (OTC) monograph M020: Sunscreen Drug Products for OTC Human Use. 24 September 2021. https://
dps-admin.fda.gov/omuf/omuf/sites/ omuf/files/primary-documents/2022-09/ Proposed%20Administrative%20 Order%20OTC000008_Amending%20 M020_Sunscreen_Signed24Sept2021.pdf
March 2025 PERSONAL CARE
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