Formulation Review: Gel Moisturizer

Based on the percentages provided, your formula contains a high proportion of occlusive ingredients (Dimethicone 100Cs, Cyclopentasiloxane, and Shea Butter Melt) totaling 42.5%. The listed water content is 25%. This composition is quite unusual for a typical light gel texture, which usually has a much higher water phase and lower oil/silicone content.

Here are the answers to your specific questions:

1.) Is the formula too liquid or too viscous? How to fix it?

Given the high percentage of silicones and oil (42.5%), the formula is likely to be quite viscous and feel more like a silicone-heavy serum or even a balm rather than a light gel. The texture will likely be smooth due to the silicones but may feel heavy or oily, not a refreshing, non-thick gel.

• How to fix: To achieve a lighter gel texture, you would need to significantly reduce the percentage of the oil and silicone phase (Dimethicone 100Cs, Cyclopentasiloxane, Shea Butter Melt) and increase the water phase (DI Water). You may also need to adjust the type and amount of gelling agent (Xanthan Gum) or consider using a different gelling system more suitable for the desired light gel texture and compatibility with other ingredients.

2.) If there is Prebiotic, is it unnecessary to add preservatives?

No, the presence of Prebiotic (Prebio-care) does not mean you can omit preservatives. Prebiotics are ingredients that nourish beneficial microorganisms on the skin. However, they do not protect the cosmetic product itself from contamination by harmful bacteria, yeast, and mold. Water-based formulations are particularly susceptible to microbial growth. A broad-spectrum preservative system is essential to ensure the safety, stability, and shelf-life of your product. The description for Xanthan Gum also notes that it does not contain preservatives and requires them in the formula.

3.) Is the emulsifier sufficient?

The emulsifier you've chosen, Lauryl PEG-9 Polydimethylsiloxyethyl Dimethicone, is a W/Si or W/O emulsifier suitable for formulas with a water ratio of 70-99% (meaning the oil/silicone phase is 1-30%). Your current formula has an oil/silicone phase of 42.5% (Dimethicone 100Cs 27.5% + Cyclopentasiloxane 10% + Shea Butter Melt 5%). Using this emulsifier with such a high oil/silicone load is outside its recommended usage range and will likely lead to emulsion instability and separation.

• How to fix: If you proceed with a high oil/silicone phase, you would need to use a different emulsifier or a combination of emulsifiers specifically designed for high oil load W/Si or W/O emulsions, potentially at a higher concentration than 2%. Alternatively, as suggested in point 1, reducing the oil/silicone phase to be within the recommended range for Lauryl PEG-9 Polydimethylsiloxyethyl Dimethicone would make this emulsifier suitable.

4.) Should the skin penetration enhancer be changed or is there another one to use?

Your formula includes Hydrogenated Lecithin (Phospholipid) and TransMoist™ (PPG-24-Glycereth-24), both of which can function as penetration enhancers or delivery aids.

• Hydrogenated Lecithin (3%) can help encapsulate ingredients to improve absorption and solubility.
• TransMoist™ (2%) is specifically described as helping to bring ingredients into the skin and improving absorption speed.
  Both ingredients are suitable for aiding penetration and are used within typical ranges. Whether you need to change them or add others depends on the specific delivery goals for your active ingredients and the final adjusted formula composition. The current combination is reasonable, assuming the overall formula is stable. If you significantly change the formula composition (e.g., make it more water-based), you might re-evaluate if these are still the most optimal choices or if others would be more effective.

In summary, the main challenges with this formulation for a "light gel" are the high oil/silicone content and the suitability of the emulsifier for this high oil load, which will likely affect both the texture and stability. Addressing these points is crucial to achieve the desired product characteristics.