Troubleshooting Issues in Lactic Acid Gel Formulation: Odor, Air Bubbles, and Pilling

Subject: Feedback on Lactic Acid Gel Formulation

Thank you for sharing your gel formulation and the issues you encountered. Let's address your questions:

1. Odor: You mentioned a strong, slightly off odor despite adding Eucalyptus Oil, and you suspect Hydroxyethyl Cellulose. As the staff member suggested, the characteristic odor is more likely coming from the Lactic Acid itself. Different batches or types of Lactic Acid can have varying odor profiles. Hydroxyethyl Cellulose is generally considered odorless or has a very mild, non-pungent odor. Your previous experience with Propolymer might be different because Propolymer (often an acrylate crosspolymer) has different chemical properties and might interact differently with other ingredients or have its own subtle scent profile that masked other odors. The staff's request for the Lactic Acid lot number is a good step to check for any unusual odor issues with that specific batch.

2. Air Bubbles: Air bubbles are very common when mixing gel formulations, especially when incorporating powder thickeners like Hydroxyethyl Cellulose into water. They get trapped during the mixing process. To minimize air bubbles:

   • Mix slowly and gently, avoiding vigorous whipping.
   • After mixing, let the gel sit undisturbed for several hours or overnight. The bubbles will often rise to the surface and dissipate.

3. White Residue (Pilling): The white, streaky residue you see on the skin is known as "pilling." This is a common issue with gel or serum formulations, particularly those containing high concentrations of polymers or thickeners like Hydroxyethyl Cellulose. It happens when the ingredients don't fully absorb or form a smooth film on the skin, instead rubbing off as small particles. Possible causes include:

   • High Thickener Concentration: 2% Hydroxyethyl Cellulose can be quite high depending on the specific grade, potentially leading to pilling.
   • Ingredient Interactions: The combination of Hydroxyethyl Cellulose with other ingredients like Glycerin, Propylene Glycol, or even the Lactic Acid at a low pH might contribute to pilling.
   • Application Method: Applying too much product or rubbing it too vigorously can cause pilling.
   • Layering: If you apply other products (like moisturizer or sunscreen) on top before the gel is fully absorbed and dry, it can also cause pilling.

   To potentially fix this:

   • Try reducing the concentration of Hydroxyethyl Cellulose slightly in a test batch, if possible, while still achieving a usable gel consistency.
   • Ensure all ingredients are fully dissolved and well-mixed.
   • Apply a very thin layer of the gel to the skin and pat gently rather than rubbing.
   • Allow the gel to fully dry before applying any other products.

It's great that you are experimenting with formulations! Troubleshooting these issues is part of the process.