Gritty Texture in Sunscreen Cream

Hi, regarding the gritty texture in your sunscreen formula after about a week, the most likely cause based on your ingredients is the precipitation of Ensulizole (Phenylbenzimidazole Sulfonic Acid).

Ensulizole is a water-soluble UV filter, but it is a weak acid and its solubility is highly dependent on pH. It needs to be neutralized to dissolve properly in water.

If the pH of your final formulation is too low, or if the pH decreases over time, the Ensulizole can come out of solution and form small crystals, which you feel as grittiness.

Recommendations:

• Check the pH of your finished cream immediately after making it and again after a week. Ensure the pH is within the recommended range for Ensulizole solubility (check your supplier's specifications, but typically slightly acidic to neutral).
• If the pH is too low, you may need to adjust it upwards slightly using a suitable base (like a dilute NaOH or Triethanolamine solution) during manufacturing.
• Ensure the Ensulizole was fully dissolved and neutralized during the manufacturing process.
• While less likely to cause hard grittiness, ensure the Bisoctrizole (Tinosorb M) dispersion was stable and well-incorporated.
• Check storage conditions to avoid extreme temperature fluctuations.