Feedback on Your Exfoliating and Dark Spot Serum Formula

Thank you for sharing your formula! It's a comprehensive approach targeting exfoliation, dark spots, and hydration, incorporating ingredients you've had positive experiences with. Here's an evaluation of the proposed concentrations and some recommendations:

Ingredient Concentrations

• Azelaic Acid (Liquid Azelaic™) 15%: This is higher than the typically recommended usage rate of 5-10% for this specific form. While Azelaic Acid is effective for dark spots and acne, using it at 15% in combination with other exfoliants might increase the risk of irritation, especially since you experienced redness with Skinoren.
• Urea 10%: This concentration is effective for both moisturizing and providing exfoliation. Your inclusion of Gluconolactone at 1.5% is appropriate for stabilizing Urea and helping to control the formula's pH.
• Sodium PCA 5% and Sodium Lactate 5%: These are excellent humectants and components of the skin's natural moisturizing factor (NMF). Sodium Lactate at 5% also contributes to skin cell turnover. The concentrations are on the higher side of typical recommendations for Sodium PCA (0.5-2%) but within the range for Sodium Lactate (2-10%). Using them together with Urea provides synergistic moisturizing benefits. However, these are electrolytes and can affect the texture created by Pro Polymer.
• Pro Polymer 3%: This amount is likely needed to create a gel texture, especially with the presence of electrolytes like Sodium PCA and Sodium Lactate. The final texture might be quite thick, potentially like a pudding.
• Gluconolactone 1.5%: This PHA provides gentle exfoliation and, as mentioned, is helpful for stabilizing Urea and pH.
• Phenoxyethanol 1%: This is a standard and effective preservative concentration.
• Allantoin 0.3%: This is a good inclusion to help soothe potential irritation from the exfoliating ingredients.

pH Consideration

The pH of your final formula is crucial for the stability and effectiveness of the ingredients, as well as minimizing irritation.

• Azelaic Acid (Liquid Azelaic™) works best in a pH range of 5-11.
• Urea stabilization with Gluconolactone is optimized around pH 4-5.5.
• Gluconolactone's exfoliating effect is better at lower pH (3.4-4.5).
• Allantoin is stable in the range of 4-8.

Aiming for a final pH in the range of 4.5-5.5 would be a reasonable balance to ensure the efficacy of Azelaic Acid and Gluconolactone while maintaining Urea stability and minimizing irritation. You will need to measure the pH of your final mixture and adjust it if necessary using a dilute acid (like Lactic Acid or Citric Acid solution) to lower the pH or a dilute base (like Sodium Hydroxide solution) to raise it.

Recommendations

1. Consider reducing Azelaic Acid: To potentially reduce the risk of irritation, especially for full-face application, you might consider starting with a lower concentration of Azelaic Acid (Liquid Azelaic™), such as 8-10%. You can always increase it later if your skin tolerates it well.
2. Consider reducing Sodium PCA: Reducing Sodium PCA to the recommended 0.5-2% range might be sufficient for moisturizing benefits and could help with the formula's texture and interaction with Pro Polymer.
3. Adjust Pro Polymer as needed: The amount of Pro Polymer might need fine-tuning depending on the desired final texture after all ingredients are incorporated.
4. Measure and adjust pH: This is a critical step. Ensure the final pH is in the 4.5-5.5 range for optimal results and reduced irritation.
5. Patch Test: Before applying the formula to your entire face, perform a patch test on a small, inconspicuous area to check for any adverse reactions.
6. Sun Protection: Always use broad-spectrum sun protection daily when using products with exfoliating ingredients.

Your formula has a strong foundation for addressing your skin concerns. By carefully considering the concentrations and pH, you can create a product that is both effective and well-tolerated.