Molecular size and absorption by the skin

Does it matter how far a molecule will go inside the skin? It depends.

Sometimes medications are better if applied topically. If you apply a medication (hormone, for example) in a patch, it is very important that the medication will penetrate the skin in a consistent way, otherwise, the dose reaching the blood would vary too much to be useful. Extensive studies are conducted to ensure that the composition of the patch is the right one to facilitate the absorption of the medication, including “delivery systems”.

For skincare

Some ingredients should stay “outside”, like sunscreen ingredients (zinc oxide, oxybenzone), for example, or substances used to substitute for a damaged skin barrier (petrolatum, silicones).

Some ingredients are meant to penetrate the skin

If you apply amino acids to your skin, you probably want them to end up inside live cells contributing to the building of new proteins. Don’t worry, some of those amino acids will go all the way where they are needed, in this case, you don’t need 100% delivery.

Hyaluronic acid, a huge molecule, is used to help prevent water loss from the skin. You don’t need to absorb it, you make your own hyaluronic acid. Giving our skin small pieces obtained by breaking up hyaluronic acid may be counterproductive because they act as signals telling the skin that there has been damage and inflammation should ensue.

Don’t be mistaken, our skin is not impermeable

The outermost layer of the skin, the stratum corneum, limits water loss from the body to the environment and allows us, humans, organisms that depend totally on water, to walk around in the Arizona desert. The stratum corneum also limits water and chemicals penetration into the skin, slowing absorption of nutrients (and harmful chemicals) applied topically. “Limits penetration” doesn’t mean that this layer is impermeable, as shown by trans-epidermal water loss. You can measure water loss across the skin with a laboratory instrument, and this water loss increases with age and skin damage. In skin aged by sun exposure, absorption of external nutrients and water loss will be higher than in young skin.

Sometimes people cite a “rule” that says molecules bigger than a specific molecular weight can’t enter the skin.  There is no research proving that assertion, it’s just a “rule.”  Some people keep forgetting that you need more than a theory (or a rule); science requires observation and experimentation.

The absorption of water-soluble nutrients through the skin will increase with skin humidity, so it’s a good idea to take advantage of the skin’s higher permeability after a shower or bath. Amino acids are electrically charged molecules, but when delivered in cream, an emulsion of water and oil containing other nutrients and salts, this property should not preclude penetration. This reasoning led to our using the amino booster in an easily applied cream rather than a serum. Even a low uptake of amino acids applied topically should substantially improve the health of skin deprived of nutrients by decreasing blood supply to the dermis that occurs to all of us when we age. And this is valid for all useful actives applied topically: you don’t need to absorb 100% of them, so forget about delivery systems. You don’t special delivery; your skin is permeable enough.