Discrepancy between Simulated and Claimed SPF/PA Values in Sunscreen Formulation
Question
Based on a sunscreen formula inspired by KANEBO ALLIE EX UV PROTECTOR GEL (MINERAL MOIST) N SPF 50/PA++++, containing:
- Zinc Oxide 200nm EasyDisperse™ (9.2%)
- OMC (7.5%)
- DHHB (2.5%)
When simulating the SPF/PA values using a tool like BASF, the result is significantly lower (around SPF 15) compared to the claimed SPF 50 PA++++ of the original commercial product.
Could you please explain the reasons for this discrepancy between simulated values and claimed values? Specifically, how do different SPF/PA testing standards and the overall formulation (beyond just the active ingredients and their percentages) affect the final SPF/PA value?
Answer
Understanding SPF and PA Values in Sunscreen Formulations
Thank you for your question regarding the sunscreen formulation from the forum post, which uses Zinc Oxide 200nm EasyDisperse™, OMC, and DHHB.
You've observed that using a sunscreen simulator like the BASF tool yields a much lower SPF (around 15) than the claimed SPF 50 PA++++ for the formula, which is based on a commercial product (KANEBO ALLIE). This discrepancy is common and highlights the difference between theoretical calculations and real-world performance.
Why Simulator Results Differ from Claimed Values
- In Vivo Testing: SPF and PA values are primarily determined by in vivo (on-skin) testing according to specific international standards (like ISO, FDA, or Japanese standards). These tests measure the actual protection provided by the finished product when applied to human skin.
- Formulation Effects: The base formulation (emulsion type, other ingredients, film-forming properties) significantly impacts how the UV filters disperse on the skin and form a protective layer. A well-formulated product can achieve higher protection than predicted by simply summing the theoretical contributions of individual filters.
- Ingredient Interactions & Synergy: UV filters can interact with each other and other ingredients in the formula. Sometimes, there is a synergistic effect where the combination provides better protection than expected. DHHB, for example, is known to be an excellent UVA filter and can also act as an SPF booster for UVB filters like OMC, as noted in its product description.
- Specific Ingredient Grades: Different grades or forms of the same active ingredient (like different particle sizes or coatings for Zinc Oxide) can have varying efficacy. Zinc Oxide 200nm EasyDisperse™ is designed for easy dispersion, which is crucial for achieving uniform coverage and optimal protection.
- Testing Standards: Different regions and manufacturers use different testing standards, which can result in varying reported SPF/PA values for similar formulations.
The Specific Formulation
The formula you mentioned uses:
- Zinc Oxide 200nm EasyDisperse™ (9.2%): A physical filter providing broad-spectrum UVA/UVB protection.
- OMC (7.5%): An organic filter primarily protecting against UVB.
- DHHB (2.5%): An organic filter primarily protecting against UVA, also acting as an SPF booster.
While the percentages might seem low for SPF 50 in a simulator, the combination of these filters, especially with DHHB acting as a booster, and the specific formulation base of the original commercial product, could potentially yield a higher SPF value in in vivo testing compared to a simple calculation.
Conclusion
The SPF 50 PA++++ claim for the original KANEBO product is likely based on their official in vivo testing according to Japanese standards. While the percentages in the formula you found are based on that product's ingredient list, simply mixing these ingredients at these percentages does not guarantee the same SPF/PA values. Achieving SPF 50 PA++++ would require careful formulation and validation through in vivo testing.
Sunscreen simulators are useful tools for initial formulation guidance and understanding the relative contributions of filters, but they do not replace actual performance testing.
