Formulation Evaluation

Your proposed formula for a gentle sulfate-free shampoo with oils and essential oils is a good starting point. The ingredients you've chosen are generally suitable for a mild cleansing product aimed at being gentle on the scalp.

• Sulfate-Free No-Tear Foaming Base (30%): This is an excellent choice for a gentle, sulfate-free shampoo base. The recommended usage rate for shampoo is 25-35%, so 30% is well within the effective range and should provide good foaming and cleansing without being harsh.
• SugarThick™ (2%): This thickener is compatible with sulfate-free systems and is derived from natural sources, aligning with a gentle formula concept. 2% is within the recommended usage range and should help achieve a desirable gel texture. It can also help reduce irritation from harsh detergents, although this base is already sulfate-free.
• Sweet Almond Oil or Argan Oil (8%): Both Sweet Almond Oil and Argan Oil are nourishing oils beneficial for moisturizing the hair and scalp. Including 8% oil in a shampoo requires a good emulsifier to ensure it disperses properly and doesn't separate or leave a greasy residue.
• Rose Hip Oil (2%): Rose Hip Oil is known for its skin-repairing and moisturizing properties. Adding 2% can contribute to scalp conditioning. (Note: You mentioned Rosemary Oil but linked to Rose Hip Oil. This evaluation assumes you intended to use Rose Hip Oil based on your link).
• Peppermint Oil (1%): Peppermint Oil provides a refreshing sensation and is sometimes used for its potential stimulating properties on the scalp. While 1% is a common usage rate for essential oils in wash-off products, it's important to consider that essential oils can be irritating for very sensitive individuals. For a "gentle" formula, you might consider a slightly lower percentage or omitting it if sensitivity is a primary concern.
• Mild Preserved Eco™ (1%): This preservative blend is suitable for cosmetic formulas and is considered gentle. 1% is within the recommended usage range to protect your product from microbial growth.
• Purified Water (to 100%): This is the base of your aqueous phase.
• Oil Blender™ (3%): This ingredient is crucial for incorporating the oils (Sweet Almond/Argan and Rose Hip) into your water-based surfactant system. At 3%, it should function effectively as an oil blender to help emulsify the oils within the shampoo base, preventing separation.

Ingredient Compatibility: The ingredients you've selected are generally compatible with each other in a shampoo formulation, especially with the inclusion of Oil Blender™ to help emulsify the oils.

Lactic Acid for pH Adjustment

You asked about the percentage of Lactic Acid needed to adjust the pH of your sulfate-free base.

• Purpose: Lactic Acid (AHA) 90% Deodorized is used to lower the pH of the formula. The Sulfate-Free No-Tear Foaming Base has a pH of 6. For a gentle shampoo, a final pH typically between 5.5 and 6.5 is desirable, as this range is closer to the natural pH of the scalp and hair.
• Amount Needed: It is not possible to provide an exact percentage of Lactic Acid needed without testing. The amount required depends on the buffering capacity of your specific formula (how well it resists changes in pH).
• How to Adjust pH: You should add the Lactic Acid gradually to your finished formula while measuring the pH with a reliable pH meter or pH strips accurate for the target range. Add a small amount, stir well, and measure. Repeat until you reach your desired pH (e.g., 5.5-6.5).
• Usage Rate Limit: According to regulations, Lactic Acid concentration in consumer cosmetic products should not exceed 10%, and the final product pH should not be lower than 3.5. For a gentle shampoo aiming for pH 5.5-6.5, the amount of Lactic Acid needed will be significantly less than 10%, likely well below 1%.

In summary: Your formulation is well-structured for a gentle shampoo with oils. The amount of Lactic Acid needed for pH adjustment must be determined experimentally by adding it slowly and measuring the pH until your target range (5.5-6.5) is reached.

I hope this helps with your formulation!