Propylene Glycol vs. Glycerin in Face Wash

You are correct in observing differences when substituting Propylene Glycol for Glycerin in your face wash formula. Both Propylene Glycol and Glycerin are humectants, meaning they help retain moisture. However, Glycerin is generally known to be a stronger humectant and can have a more viscous, slightly "sticky" feel compared to Propylene Glycol.

In a rinse-off product like a face wash, Glycerin's humectant properties can contribute to a more hydrated feel on the skin after washing. It can also play a role in the texture and stability of the foam produced by the surfactants (like Coco Betaine and Lauryl Glucoside in your formula).

Propylene Glycol, while also a humectant and solvent, is less viscous and may not provide the same level of moisturization or foam support as Glycerin at the same concentration. This difference in properties likely explains why you observed less foam and a drier skin feel when using Propylene Glycol.

It is perfectly fine to adjust cosmetic formulas based on the desired feel and performance. Since the batch made with Propylene Glycol did not meet your expectations for a face wash, using it as a body wash is a practical and appropriate solution.

Penetration Enhancers

Regarding penetration enhancers, you are right that PE-1 Aqua is specifically designed to help water-soluble active ingredients penetrate the skin. Its description indicates it is derived from natural terpenes and is oil-soluble, but it is formulated to enhance the delivery of water-soluble compounds. It is also noted that using PE-1 Aqua with oil-soluble active ingredients is not recommended as it can hinder their absorption.

If you are looking for a penetration enhancer that can help carry oil-soluble ingredients into the skin, PE-1 Aqua is not the suitable choice.

Based on the available information, Phospholipid is a penetration enhancer that is suitable for carrying both water-soluble and oil-soluble ingredients. It is derived from natural sources (Soy Lecithin) and can also improve skin feel and provide moisturization benefits.

There are other ingredients that can act as penetration enhancers or support penetration, such as Laurocapram (primarily for water-soluble), 1,2-Hexanediol (can enhance penetration and has other functions like preservative support and humectancy), and Ethoxydiglycol (solvent and penetration enhancer). Reservoir-Tech is different; it's not a direct penetration enhancer but forms a film to slowly release actives, which can help reduce irritation.

Therefore, if you need to enhance the penetration of oil-soluble ingredients, Phospholipid would be a more appropriate option than PE-1 Aqua.