Skin Penetration and Layering Cosmetic Ingredients

Let's address your questions regarding skin penetration and the use of the same ingredient in multiple layered products.

1. Skin Penetration of Actives

The primary factor determining how well an active ingredient penetrates the skin is the nature of the ingredient itself. This includes its molecular size and its affinity for the different layers of the skin (which contain both water and oil). There is no single formula or set of ingredients that guarantees optimal penetration for all actives; it is a complex process with many variables.

While ingredients like Water, Bisabolol, Ethoxydiglycol, Isopropyl Alcohol, and Propylene Glycol can act as solvents or carriers, simply adding them does not automatically ensure better skin absorption. The overall formulation, including the base or thickener used, plays a significant role.

Regarding the use of exfoliating ingredients, incorporating ingredients that gently exfoliate, such as GlucoBright™ (Acetyl Glucosamine), can potentially help improve the penetration of other actives by removing dead skin cells on the surface. GlucoBright™ is known for its ability to exfoliate without causing irritation, unlike some other exfoliants, and also offers benefits like reducing dark spots and stimulating hyaluronic acid production.

It's important to note that the feeling of a product absorbing quickly (like disappearing into the skin) does not necessarily mean better or deeper penetration. This feeling can sometimes be due to volatile ingredients like Cyclomethicone, which evaporate quickly, rather than the active ingredients being fully absorbed into the skin layers.

Formulation is often a process of trial and error to find the best base and combination of ingredients that allow the active to perform effectively on the skin.

2. Using the Same Ingredient in Layered Products

For cosmetic ingredients, the safety and potential for irritation are primarily determined by the concentration of the ingredient in each individual product, not the cumulative amount applied from layering multiple products, as long as the concentration in each product is within the recommended safe usage rate.

For example, using a serum with 4% GlucoBright™ (Acetyl Glucosamine), followed by a lotion with 4% GlucoBright™, and then a sunscreen with 4% GlucoBright™ is generally considered safe because the concentration in each product (4%) is within the typical recommended usage rate for GlucoBright™ (1-8%, with 4% often recommended in combination with Niacinamide like Safe-B3™).

This principle differs from certain ingredients like AHA/BHA, where the total amount and frequency of application significantly impact the risk of irritation.

However, some ingredients, like DMAE (SkinTight MD™) Liquid, can cause irritation, especially on sensitive skin or at higher concentrations (above 5%). If you experience irritation, it's crucial to reduce the concentration or stop using the product containing that ingredient. The user's experience with 10% DMAE causing significant stinging, which improved after reducing the concentration, highlights this.

When formulating, you should always adhere to the recommended maximum usage rate for each ingredient in each product. While layering products with the same ingredient within these limits is generally safe from a toxicity standpoint, you should consider the overall feel and potential for skin reaction based on the total effect of the layered formulas. For instance, if a thickener like Pro Polymer™ causes a dry or tight feeling, as experienced by one user, incorporating humectants like Glycerin (typically used at 5% in general formulas) or emollients from the LipidSoft™ range can help mitigate this effect, even if the active ingredient concentration is within limits across layers. The user's success with using 8% b5 extralite to counteract the dryness from Pro Polymer™ is another example of adjusting the overall formula to improve skin feel.