When you are meeting with a cosmetic raw material supplier, they often talk about how their ingredient will penetrate the skin. Even cosmetic marketers use the phrase “skin penetration” when advertising skin and anti-aging products. Penetration seems to be an important characteristic of cosmetics but have you ever thought about why anyone would want a cosmetic ingredient to “penetrate”?
What is skin penetration?
The term penetration is used to describe a characteristic of cosmetic ingredients in which they migrate from the surface of skin into the lower layers of the skin cells. Our skin is made up of a number of cell layers and some ingredients can penetrate deep into those layers. If you want your product to go below the surface of skin you want something that penetrates.
Why skin penetration
While many people tout penetration as a benefit there are only certain times you want your formulation to penetrate the skin. This would include situations in which you want to improve the feel of the formula upon application and when you want to make water resistant claims.
However, these are not the reason that most marketers (and some cosmetic chemists) desire skin penetration. Many people want their products to penetrate the skin to improve the effectiveness of the “active ingredient”. You see, there are a number of cosmetic ingredients and products that claim to interact with skin cell metabolism, increasing collagen production, or stimulating some other enzyme that will magically remove wrinkles. But the truth is if these ingredients actually could do this, the products would then be considered drugs and would require much more stringent & expensive testing (at least in the United States).
In the US any product that affects skin metabolism is a drug
Although most penetration claims are for non-cosmetic purposes, there are still legitimate reasons that you would want your formulation to penetrate the skin. And for these, it is useful to use penetration enhancer ingredients.
Typical skin penetration ingredients include emulsifiers and solvents. Emulsifiers are surfactants that have both a hydrophobic segment and a hydrophilic segment on the molecule. They allow for compatibility between polar and non-polar ingredients. In a solution, they form micelles which can surround and encapsulate “active” ingredients. When place on the skin, the emulsifiers will penetrate deeper into the skin and bring whatever is encased in the micelle with it. Emulsion penetration can be enhanced by reducing the particle size of the emulsion. So, microemulsions and nanoemulsions are excellent skin penetrating vehicles. Phosphatidylcholine is a good penetration ingredient.
Solvents like propylene glycol are also excellent penetration enhancers. They can help shuttle soluble ingredients through the lipid top layers of the skin into the lower layers.
Penetration enhancing caution
There are times when you do not want your cosmetic to penetrate. This would include products that are cleansers as they can lead to irritation and colors because you want to be able to remove them. Also, cosmetics are designed to make superficial improvements so you also don’t want your product to penetrate down as far as the dermis where the living skin cells are. Once an ingredient gets to the dermis it could interact with skin cells and affect skin metabolism. And while this is what some marketers want to claim about their products, this is not something that you want to actually have happen.