Achieving SPF 30 in a Clear Mineral Water Spray

You are looking to create a clear mineral water spray with SPF 30 using water-soluble sunscreens. Your current formula uses Bisdisulizole Disodium (2%), Ensulizole (2%), and Benzophenone-4 (2%).

Let's look at the sunscreens you are using:

• Bisdisulizole Disodium: This is a water-soluble filter that primarily provides UVA protection.
• Ensulizole (Phenylbenzimidazole Sulfonic Acid): This is a water-soluble filter that is effective for UVB protection and contributes to the SPF value. It is suitable for clear, water-based formulas and can be used up to 8%.
• Benzophenone-4: This is also a water-soluble filter, often used to protect the formula itself from UV degradation. It provides some UVB protection but does not contribute significantly to a high SPF value and is typically used as a secondary filter for skin protection, allowed up to 5%.

Determining the exact SPF of a combination of sunscreens requires laboratory testing (in-vivo or in-vitro) on the final formulation. It is not possible to simply add the SPF contributions of individual filters.

However, based on the typical efficacy of these filters, your current formula with 2% Ensulizole and 2% Benzophenone-4 likely provides an SPF significantly lower than 30. Ensulizole is the main SPF contributor among the three, and 2% is generally not sufficient to reach SPF 30 on its own.

To achieve SPF 30 or close to it in a clear water-based spray using water-soluble filters, you would typically need higher concentrations of effective UVB filters. You could consider increasing the concentration of Ensulizole up to its maximum allowed limit (8% in Thailand/EU). Combining it with other compatible water-soluble or easily dispersible filters that contribute to SPF might also be necessary. Always ensure the chosen filters are compatible with a clear, water-based system and adhere to local regulations.

Remember that achieving a specific SPF target requires formulation expertise and validation through testing.