Adding Zinc Oxide to Homemade Sunscreen Formulation

Question

Hello,

I currently use three products that I really like and want to make them myself using ingredients I have purchased quite a lot of.

I am currently using a Vitamin C serum based on the formula recommended by Khun C7 in the Skin Care Formula Hub, but I have made some adjustments:

I adjusted the pH to ~2.5-3.
I added AHA (both 88% and 100% types). I honestly didn't measure exactly how much, but I know I added quite a bit because I initially added too much base (3.0g instead of 2.5g as per the formula), resulting in a pH of ~5-6. It was very difficult to lower the pH, requiring a significant amount of AHA.
I used Double Hyaluron instead of Nano and Standard types for moisturization.

I have used this serum on my face without any issues; I don't feel any stinging, itching, or increased sun sensitivity. I feel quite indifferent, maybe my skin is very resilient.

I use it day and night. During the day, I apply a lot of sunscreen and rarely go out. When I do go out, I wear a hat, glasses, mask, and a hooded jacket over the hat. Even when staying home, I apply sunscreen.

I don't mind if the sunscreen leaves a white cast; I want it to be like Smooth E's formula.

Based on their formula, I was wondering if I should add Zinc Oxide? I see it listed as the last ingredient. I have read about SPF and PA values from Khun C7's previous posts.

Thank you very much.

MySkinRecipes Expert · Accepted Answer

Zinc Oxide in Sunscreen Formulations

While the exact percentage in commercial products like Smooth E is not available, Zinc Oxide is a key ingredient in many physical sunscreens.

Function: Provides broad-spectrum protection against UVA and UVB rays.
Types for Sunscreen: Look for coated powders or liquid dispersions designed for sunscreen use to minimize whiteness and ensure proper dispersion.
Typical Usage Rate: Varies depending on the type of Zinc Oxide and desired SPF/PA level. Powder forms are often used at 5-25%, while dispersions (containing active Zinc Oxide) might be used at higher percentages (e.g., 5-50%), keeping in mind the regulatory limit for active Zinc Oxide (25% in the US, check local regulations).
Combination: Often used with Titanium Dioxide for complete broad-spectrum coverage.

You can choose a suitable type of Zinc Oxide based on your formulation's base (oil, water, silicone) and desired texture, and start experimenting within the recommended usage ranges to achieve your desired level of protection.

Regarding your question about adding Zinc Oxide to your formula to be like Smooth E, yes, if you are aiming for a physical sunscreen similar to Smooth E (which likely uses physical filters), incorporating Zinc Oxide is essential. You would need to formulate a complete sunscreen base that properly disperses and stabilizes the Zinc Oxide (and potentially Titanium Dioxide) to achieve effective and stable UV protection. Simply adding Zinc Oxide powder to an existing formula not designed for it may not result in effective or stable sunscreen.

Regarding your Vitamin C serum, it's good that your skin tolerated the adjustments, but it's generally recommended to follow tested formulas and usage rates, especially when dealing with potent ingredients and pH adjustments, to ensure efficacy and safety.

I hope this information helps you with your sunscreen formulation project!