Toner formulation with AHA/BHA: concentration, preservation, Polysorbate 20, and pH

Hello chakimyu,

Thank you for providing your revised formula and explaining your experience with commercial products. It's good that you are incorporating soothing ingredients to mitigate potential irritation.

Regarding your formula:

• Exfoliant Concentration: Your revised formula contains a total of 10% AHA (4% Mandelic, 3% Glycolic, 3% Lactic) and 10% Willow Bark Extract (which contains natural salicylates, acting similarly to BHA). While you tolerate a commercial product with 10% AHA and 2% BHA, the combination and specific forms/concentrations in a DIY formula can behave differently. This is still a high concentration of exfoliants, and it may cause irritation, especially if your skin's condition changes or if used daily. It is highly recommended to perform a patch test before applying it to your entire face. You might also consider starting with lower concentrations of the exfoliating acids, as the staff previously advised, and gradually increasing if your skin tolerates it.
• Preservation: As the staff mentioned previously, the preservative in Witch Hazel is not sufficient to preserve the entire formula, especially with a high water content and various extracts. You absolutely need to add a broad-spectrum preservative system to prevent microbial growth and ensure the product is safe to use.
• Polysorbate 20: Polysorbate 20 is a solubilizer often used to help disperse small amounts of oil-soluble ingredients or extracts into a water-based formula like a toner. Your proposed method of mixing Polysorbate 20 with any oil-soluble components before adding to the water phase is a correct approach for solubilization. However, as the staff noted, depending on the solubility of your specific extracts and other ingredients, Polysorbate 20 might not be strictly necessary. If all your ingredients are sufficiently water-soluble, you could potentially omit it. If you include it, 5% seems quite high for a toner unless you have significant oil-soluble components to solubilize.
• pH Adjustment: As the staff emphasized, the final pH of the formula is critical, especially when using AHAs. AHAs are most effective at lower pH levels (typically below 4.0), but a very low pH increases the risk of irritation. The pH also affects the stability of other ingredients, such as Allantoin and potentially some extracts. You must measure and adjust the final pH using Citric Acid (to lower pH) or Triethanolamine (to raise pH) to a level that balances efficacy, irritation potential, and ingredient stability. A pH between 3.5 and 4.0 is often targeted for AHA products, but you should test what your skin tolerates.

In summary, your revised formula includes good soothing ingredients, but the high concentration of exfoliants requires caution and patch testing. Adding a preservative is essential. You should verify if Polysorbate 20 is truly needed based on ingredient solubility and carefully measure and adjust the final pH.