Formulation Advice: Salicylic Acid in Your Formula

Regarding your formula and the inclusion of 2% Salicylic Acid liquid, here is our advice:

1. Salicylic Acid Concentration: Including 2% active Salicylic Acid is the maximum concentration permitted by the FDA for leave-on cosmetic products. So, from a regulatory standpoint, this concentration is acceptable.

2. Potential for Irritation: While 2% Salicylic Acid is effective for exfoliation and acne treatment, it can cause irritation, especially on sensitive skin. Your formula includes several soothing ingredients such as Niacinamide (Vitamin B3), Allantoin, Dipotassium Glycyrrhizate, Zinc PCA, Centella Asiatica Extract, and Aloe Vera Extract. These ingredients are beneficial and can help mitigate some of the potential irritation from Salicylic Acid.

3. Importance of pH: The efficacy and irritation potential of Salicylic Acid are highly dependent on the formula's pH. Salicylic Acid is most effective at a low pH (ideally around 3-4), but this can significantly increase irritation. Furthermore, other ingredients in your formula, like Niacinamide and Zinc PCA, have optimal pH ranges (Niacinamide 4.0-7.0, Zinc PCA 4-6 for solubility). To balance efficacy, irritation, and ingredient stability, we recommend checking and adjusting the final pH of your formula to be in the range of 4.0-5.0. This range allows Salicylic Acid to be reasonably effective while minimizing irritation and maintaining the stability of other beneficial ingredients.

4. Formula Stability: You mentioned that your test formulation did not show separation, which is a good sign. HPMC is generally compatible with many active ingredients, including some forms of liquid Salicylic Acid, which likely contributes to the stability you observed.

In summary: You can include 2% Salicylic Acid liquid in your formula as it is within the regulatory limit for leave-on products. However, irritation is possible depending on skin type and the final pH. We strongly recommend checking and adjusting the pH to the 4.0-5.0 range to optimize the balance between efficacy and skin comfort. The soothing ingredients in your formula will also help.