Analysis of Your Cream Formulation Issue

Based on your description and the previous discussion, the stinging sensation and gritty feeling you experience when applying and rubbing the cream are likely due to a combination of factors related to the ingredients and potentially their interaction or incomplete dissolution.

Potential Causes:

1. DMAE Concentration and Irritation: As discussed previously, DMAE, especially at a high concentration of 10%, is known to cause skin irritation, redness, and a tingling or stinging sensation in some individuals, particularly those with sensitive skin. The test conducted by the staff, even with a simpler mixture containing DMAE and other ingredients, still resulted in irritation for some users, strongly suggesting DMAE as a primary culprit for the stinging.

2. Gritty Texture (Crystallization or Incomplete Dissolution): The gritty feeling is likely caused by solid particles in the cream. This could be due to:

   • Incomplete dissolution of powder ingredients: L-tyrosine and DMAE were used in powder form. If these powders are not fully dissolved in the water phase before emulsification, they can remain as fine crystals or particles in the final product, causing the gritty texture.
   • Crystallization over time: Some ingredients, even if initially dissolved, can crystallize out of the solution over time, especially if the formula is not stable or stored improperly. The pH of 4.5-5 is within the typical range for many cosmetic formulations, but the specific combination of ingredients might lead to crystallization issues.

3. Interaction of Ingredients: The combination of multiple active ingredients and emulsifiers/thickeners could potentially lead to incompatibilities or interactions that affect solubility or stability, contributing to both irritation and texture issues.

Suggested Solutions:

1. Reduce DMAE Concentration: Lowering the concentration of DMAE powder to 3-5% is recommended to significantly reduce the potential for irritation, as suggested by the staff. While this might slightly reduce the anti-aging efficacy, it can greatly improve skin comfort.

2. Ensure Complete Dissolution of Powders: Pay extra attention to fully dissolving all powder ingredients (L-tyrosine, DMAE powder, EDTA, Sodium Hyaluronate, Pep-Coll, Vitamin B3, Green Tea Extract) in the water phase before combining with the oil phase. Gentle heating and sufficient mixing time in the water phase are crucial for this.

3. Consider Ingredient Form: If the gritty texture persists, consider using liquid forms of ingredients if available and suitable for your formulation, such as a liquid form of DMAE.

4. Optimize Emulsification and Thickening: While your base formulation has worked before, the addition of new active ingredients might require adjustments to the emulsifier and thickener system to ensure a stable and smooth texture that can keep all ingredients properly dispersed.

5. Review pH Adjustment: Ensure the Triethanolamine is effectively and evenly dispersed to adjust the pH. While the final pH is within a reasonable range, localized pH variations during mixing could potentially affect ingredient solubility.

By addressing the concentration of DMAE and ensuring all powder ingredients are completely dissolved and the formulation is stable, you should be able to reduce both the stinging sensation and the gritty texture.