Precipitation Issue in Lactic Acid Toner Formulation at Low pH

It seems you're experiencing precipitation in your Lactic Acid toner formulation after adding Mild Preserved Eco, likely due to the very low pH of 2.

Here are the answers to your questions:

• If pH is 2, can it be used on the face?
  No, a pH of 2 is generally too low for cosmetic products applied to the face. It is highly acidic and can cause significant skin irritation, redness, or even chemical burns, especially with an AHA like Lactic Acid. The recommended pH range for AHA products is typically between 3.5 and 4.0 to ensure efficacy while minimizing irritation.
• If not, what should be used to adjust the pH?
  You should adjust the pH upwards using a basic solution, such as a dilute solution of Sodium Hydroxide (NaOH). Add it drop by drop while mixing and checking the pH until you reach your desired range (e.g., 3.5-4.0).
• Can TaraGel be added to the mixture that has already precipitated to create texture?
  Adding TaraGel to a mixture that has already precipitated is unlikely to fix the issue or create a stable texture. The precipitation indicates an incompatibility or instability in the current mixture, most likely the Mild Preserved Eco at pH 2. It's best to correct the formulation issues first.
• Or if making a new batch, is a preservative necessary? The pH is 2.
  Yes, a preservative is still necessary even at a low pH like 2. While low pH can inhibit some microbial growth, it doesn't protect against all types, such as molds and yeasts. Furthermore, the formulation contains water and other nutrients. The precipitation you observed with Mild Preserved Eco at pH 2 suggests it is not suitable for this pH. You need to select a preservative that is effective and stable in your final desired pH range. If you adjust the pH to 3.5-4.0, you should check the specifications of Mild Preserved Eco or other preservatives for their recommended pH range.

The precipitation likely occurred because Mild Preserved Eco (Ethylhexylglycerin and Caprylyl Glycol) is not stable or soluble at such a low pH (2).

For a new batch, I recommend:

1. Mix water, Lactic Acid, Disodium EDTA, and Dimethyl Isosorbide.
2. Adjust the pH to your target range (e.g., 3.5-4.0) using a dilute Sodium Hydroxide solution.
3. Once the pH is stable, add TaraGel and mix until dispersed/hydrated.
4. Finally, add a preservative that is suitable for your final pH. Check the specifications of Mild Preserved Eco or other preservatives for their recommended pH range.