90 SUN CARE
TABLE 4: COMPOSITION OF FORMULATION 1 (ADVANCED NATURE SILK PREMIUM SUNSCREEN)
Phase INCI name (Trade name) A Water
Sodium Chloride Propane diol Preservative
B1
G-Block DZ 370 CCT Zinc Oxide (and) Caprylic/Capric Triglyceride (and) Polyhydroxystearic Acid (and) Polyglyceryl-3 Polyricinoleate (and) Isostearic Acid (and) Lecithin
AppleCare PDS 300 Polyhydroxystearic Acid (and) Caprylic/Capric Triglyceride (and) Isostearic Acid (and) Lecithin (and) Polyglyceryl-3 Polyricinoleate
G-Gel ECO-HMS C13-15 Alkane (and) Quaternium-90 Bentonite (and) Triethyl Citrate
B2 Ethyl Macadamiate (Floramac 10) C13-15 Alkane (Hemisqualane)
C
Polyglyceryl-4 Diisostearate/ Polyhydroxystearate/ Sebacate (Isolan GPS)
produced the lowest in vitro SPF values. The median SPF values from the DPM were 11.9 for Formulation 1 and 16.6 for Formulation 2, which are considerably lower than the corresponding in vivo SPF values (51.1 for Formulation 1 and 44.6 for Formulation 2), covering only 23.3% and 37.2% of their respective in vivo SPF values for each formula. This discrepancy suggests that Formulation
2 showed a better correlation with in vivo results compared to Formulation 1, potentially indicating that the DPM is more effective with coated-ZnO dispersions. However, the substantial SPF difference between in vitro and in vivo testing highlights fundamental variations in how different SPF testing methods evaluate sun protection. Despite this underestimation, the DPM retains the typical advantages of in vitro testing, including high precision and reproducibility. When comparing overall in vivo SPF values,
Formulation 1 demonstrates higher median SPF (51.1) than Formulation 2 (44.6). Formulation 1 also exhibits greater variability, with the IQR of 18.15 compared to 12.9 for Formulation 2. Although Formulation 2 achieves a
slightly higher maximum SPF (69 versus 67), Formulation 1 has a higher minimum SPF (44.6 versus 39.9). The results suggest that Formulation 1, which contains uncoated ZnO dispersion, may provide more consistent baseline protection across different skin types. In contrast, Formulation 2, which uses coated ZnO dispersion, exhibits greater variability but has the potential for higher maximum protection in certain skin types. The in vitro testing results reveal interesting
contrasts between the two formulations. While both formulations show identical statistical measures under the ISO 24443 method, the DPM clearly distinguishes between them. Formulation 2 achieves a median SPF of 16.6 under the DPM, which is 39% higher than the median SPF of 11.9 for Formulation 1. Further
PERSONAL CARE November 2025
w/w (%) 20.9 0.80 3.00 0.30
35.0 2.00 2.50
15.5 18.0
2.00 C B
TABLE 5: COMPOSITION OF FORMULATION 2 (STRESS FREE SUN ELIXIR) Phase INCI name (Trade name)
A Water Propanediol Biosaccharide Gum-1 (Fucocert)
Propanediol (and) Aqua (and) Sophora Japonica Flower Extract (Resistress)
Magnesium Sulfate Preservative
S-Block DZ CocoDerm Zinc Oxide (and) Coco-Caprylate/Caprate (and) Triethoxy- caprylylsilane (and) Polyhydroxystearic Acid (and) Polyglycer- yl-3 Polyricinoleate (and) Lecithin
Dicaprylyl Carbonate (Cetiol CC) Undecane (and) Tridecane (Cetiol Ultimate)
G-Gel ECO-HMS C13-15 Alkane (and) Quaternium-90 Bentonite (and) Triethyl Citrate
Polyglyceryl-4 Diisostearate/Polyhydroxystearate/Sebacate (Isolan GPS)
studies are needed to evaluate this difference in greater detail.
Challenges and implications for SPF testing Differences between in vitro and in vivo SPF testing create both regulatory and product development challenges, raising concerns about a one-size-fits-all approach for SPF evaluation. Relying solely on in vitro testing risks undervaluing high-ZnO sunscreens, which could slow mineral sunscreen innovation and limit consumer options. The in vitro standard of 1.3 mg/cm2
also does not reflect actual consumer
behavior, where sunscreen is applied by sight, resulting in variable, volume-based coverage. This discrepancy can also lead to economic
challenges for manufacturers and complicate product evaluation. Refining in vitro protocols to better mirror actual consumer application is essential for supporting innovation, ensuring consumer confidence, and enabling fair, science- based assessment of sunscreen efficacy. To address these challenges, several
improvements to in vitro testing are necessary. Potential refinements could include: ■ Switching to volumetric application methods to better replicate real-world consumer sunscreen application. ■ Adjusting application rates based on specific gravity to ensure proper film thickness.1 ■ Further enhancing PMMA plate designs to more accurately mimic human skin texture. ■ Controlling evaporation rates to maintain film uniformity during testing.
Conclusion As mineral sunscreens become more widely adopted, ensuring accurate SPF testing methodologies becomes increasingly urgent. Refining in vitro SPF testing will allow for a more accurate and fair assessment of ZnO-based sunscreen efficacy, ultimately benefiting both manufacturers and consumers.
Moving forward, ongoing research and
collaboration between regulatory agencies, researchers, and industry professionals will be key to establishing reliable SPF testing protocols that accurately reflect real-world sun protection performance.
PC
References 1. Osterwalder U, Hubaud JC, Perroux-David E, Moraine T, van den Bosch J. (2024). Sun- protection factor of zinc-oxide sunscreens: SPF in vitro too low compared to SPF in vivo - a brief review. Photochemical & Photobiological Sciences: Official journal of the European Photochemistry Association and the European Society for Photobiology. 2024; 23(10), 1999–2009
2. ISO 24444 (2019) Cosmetics—Sun protection test methods—In vivo determination of the sun protection factor (SPF).
https://www.iso. org/standard/
72250.html
3. US Food and Drug Administration (FDA). (2019). Sunscreen drug products for over the counter human use: proposed rule. Federal Register, 84(38), 6204–6275
4. ISO 24443 (2021) Cosmetics—Determination of sunscreen UVA photoprotection in vitro.
https://www.iso.org/standard/75059.html
5. ISO 23675 (2024) Cosmetics—Sun protection test methods — In vitro determination of sun protection factor (SPF).
https://www.iso.org/ standard/
76616.html
6. Hughes S, Lowe N, Gross K, Mark L, Goffe B, Hughes H, Cole C. Assessment of Natural Sunlight Protection Provided by 10 High- SPF Broad-Spectrum Sunscreens and Sun-Protective Fabrics. Current Problems in Dermatology. 2021; 55, 157-169
7. Dimitrovska Cvetkovska A, Manfredini S, Ziosi P, Molesini S, Dissette V, Magri I, Scapoli C, Carrieri A, Durini E, Vertuani S. Factors affecting SPF in vitro measurement and correlation with in vivo results. International Journal of Cosmetic Science. 2017; 39(3), 310–319
www.personalcaremagazine.com
w/w (%) 34.5 4.00 0.50
1.50 1.00
0.50 31.5
10.0 7.00
4.00 5.50
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