Physical Sunscreen Separation Issue After Following Recommended Recipe

Question

I followed the recommended formula for physical sunscreen from the pinned post, but the sunscreen separated. I tried making it a second time, and the same problem occurred.

The formula used is:

Zinc Oxide 200nm EasyDisperse 5%
Titanium Dioxide 200nm EasyDisperse 5%
Cyclomethicone 15%
Dimethicone 20%
Light Cream Maker 1.5%
Water 52.5%

I followed all the steps exactly, except I added a preservative:

Phenoxyethanol SA 1%

The mixing steps I followed were:

Mix ingredients 1 + 2 + 3 + 4 together and stir until combined.
Add Light Cream Maker 1.5% and stir until combined.
Gradually add 1/3 of the water, stir until combined, then add another 2/3 of the water and stir, and finally add the remaining water and stir.
Finally, add the preservative and stir.

I stirred very carefully and for a long time, fearing they wouldn't combine. Could this cause the cream to separate? (I used manual stirring, no machine). After adding all the water and the preservative, the texture was smooth at first, but after stirring for a while, the texture started to change and clump together.

Is it possible that using bottled drinking water (from 7-11) instead of distilled water caused this? I thought bottled water should be clean.

I made it this way twice. The first time I thought stirring for too long caused the separation. The second time I tried stirring quickly, but it still separated (or maybe it was still too long?). It failed both times. What did I do wrong?

MySkinRecipes Expert · Accepted Answer

Subject: Re: Help!! Mixed according to the recipe, but the sunscreen separated?

Hello,

Thank you for reaching out regarding the issue with your homemade physical sunscreen separating. It's frustrating when a formulation doesn't turn out as expected, especially after trying multiple times.

Based on the ingredients and the process you described, the separation is likely due to a combination of factors common when making physical sunscreens with high levels of powders and silicones, especially without specialized equipment.

Here are the most probable reasons for the separation:

Insufficient Mixing Energy: Physical sunscreens containing high percentages of solid particles like Zinc Oxide and Titanium Dioxide, along with silicones (Cyclomethicone, Dimethicone), require significant shear force to create a stable emulsion. Manual mixing, even if done carefully and for a long time, often does not provide enough energy to properly disperse the powders and fully incorporate the water phase into the oil/silicone/emulsifier phase. This leads to an unstable emulsion that separates over time. The clumping you observed after mixing is a sign that the emulsion is breaking. Using a high-shear mixer or homogenizer is highly recommended for this type of formulation to achieve proper dispersion and emulsion stability.
Water Quality: While bottled drinking water is clean, it contains dissolved minerals and salts that can sometimes interfere with the stability of cosmetic emulsions. Using distilled or deionized water is always recommended in cosmetic formulations to avoid potential issues caused by impurities.
Powder Dispersion: Ensure that the Zinc Oxide and Titanium Dioxide powders are thoroughly dispersed in the oil/silicone phase before adding the water phase. Clumped powders can act as stress points in the emulsion, leading to instability. Mechanical mixing helps significantly in achieving fine powder dispersion.

Regarding your specific questions:

Mixing Time: Manual mixing for too long or too short a time can contribute, but the primary issue is likely the type of mixing (manual vs. mechanical). Manual mixing may simply not be sufficient for this formula regardless of duration.
Water Type: Yes, using bottled drinking water instead of distilled water can potentially contribute to emulsion instability due to dissolved minerals.

Recommendations:

Use Distilled or Deionized Water: Always use distilled or deionized water for cosmetic formulations.
Improve Mixing: If possible, use a high-shear mixer or homogenizer, especially during the step where you combine the oil/emulsifier phase with the water phase. Ensure the powders are well dispersed in the oil phase using mechanical mixing before emulsification. If mechanical mixing is not available, achieving a stable physical sunscreen with this formula might be challenging.
Review the Original Recipe Instructions: Double-check the original recipe instructions for any specific mixing techniques or temperature requirements that might have been missed.

The addition of Phenoxyethanol SA (Optiphen Plus) at 1% at the end is a standard practice and is unlikely to be the primary cause of this severe separation, although some ingredients can sometimes affect stability. However, the fundamental issue here appears to be related to the physical process of creating the emulsion with these ingredients and concentrations using manual mixing.

I hope this explanation helps you understand the issue. Achieving stable physical sunscreens at home can be tricky without the right equipment.