Physical Sunscreen Formulation: Texture, SPF, Reapplication, and Color Adjustments

Question

I am developing a physical sunscreen formulation using the following ingredients:

Part 1 (Oil Phase):

Titanium Dioxide 15nm Liquid 20%
Zinc Oxide 35nm Liquid 8%
LipidSoft™ Matte 5%
WaterGuard™ Lite 3%

Heat all ingredients in Part 1 together to 70°C.

Part 2 (Water Phase):

Remaining Water
Phenoxyethanol SA 1%
Satin Cream Maker 1%

Heat the water phase to 70°C, then gradually add it to the oil phase while mixing.

I have the following questions:

Can this formula be mixed? Do I need to adjust or add any ingredients to achieve a light, easy-to-spread, non-greasy texture?
I don't fully understand SPF calculation. Is the amount of sunscreen agents used in this formula sufficient for daily use? I read that physical sunscreens don't need reapplication like chemical sunscreens due to higher stability. Is this formula sufficient for real-world use without reapplication? Also, I regularly use BHA. Is this formula sufficient to protect my skin from the sun while I am using BHA regularly? How else should I improve the formula?
I have yellowish skin. I've read reviews that Titanium Dioxide 15nm Liquid can give the skin a purple tone when used in high amounts. I am concerned about this. Are there any ways to fix this? Or if I should use colorants, which type should I use for easiest mixing, and at which step should I add it?

MySkinRecipes Expert · Accepted Answer

Physical Sunscreen Formulation Feedback

Regarding your physical sunscreen formulation and questions:

1. Mixability and Texture

Your initial formula has a high oil phase content (36%), which makes it difficult to emulsify properly using only Satin Cream Maker. To achieve a stable emulsion with a light, easy-to-spread, non-greasy texture, it is recommended to adjust the emulsifier system. You can use a combination of Milk Lotion Maker (4%) and Satin Cream Maker (1%).

The mixing procedure should also be adjusted. Heat both the oil phase (containing Titanium Dioxide 15nm Liquid, Zinc Oxide 35nm Liquid, LipidSoft™ Matte, WaterGuard™ Lite, and Milk Lotion Maker) and the water phase (containing water and Phenoxyethanol SA) to approximately 70°C. While continuously blending the water phase at high speed, gradually add the heated oil phase. Continue blending as the mixture cools down.

2. SPF Efficacy and Reapplication

The combination and percentages of Titanium Dioxide 15nm Liquid (20%) and Zinc Oxide 35nm Liquid (8%) in your formula provide sufficient sun protection for daily use. While physical sunscreens are generally very stable, the need for reapplication depends on factors like sweating, water exposure, and friction (e.g., wiping your face).

Your inclusion of WaterGuard™ Lite helps improve the formula's water resistance, which contributes to longer-lasting protection. For typical daily activities without excessive sweating or water exposure, reapplication might not be strictly necessary based on stability alone. However, for prolonged sun exposure, heavy sweating, or swimming, reapplication is always recommended regardless of sunscreen type to ensure continuous and adequate coverage.

Using BHA makes your skin more sensitive to the sun, so consistent and effective sun protection is crucial. Your proposed formula is considered effective enough to provide adequate protection when using BHA regularly.

3. Addressing Potential Purple Cast

While a purple cast from Titanium Dioxide 15nm Liquid is not commonly observed in testing, it can sometimes occur depending on skin tone and lighting. If you find that your formula has a purple tone on your yellowish skin, you can adjust the color by adding a small amount (1-2%) of Titanium Dioxide 200nm EasyDisperse. This ingredient is a white pigment that can help neutralize the tone and provide a brighter, more natural look. It should be mixed into the oil phase along with the other oil-soluble ingredients and heated to 70°C during the emulsification process.