Can skin-care ingredients be absorbed into skin? There is no question that they can. Of course it’s a bit of a paradox that while the skin is designed to keep substances out of the body it can also let other substances in. State-of-the-art skin-care formulations are designed to both stay on the surface and be absorbed beyond the surface to exert beneficial influences on the support systems underneath.
What all skin types need is a combination of ingredients that stay on the surface (technically in the layer called the stratum corneum), as well as penetrate to protect and supplement the lower layers of skin. The right combination includes emollients and antioxidants that stay on the surface, antioxidants and skin-identical ingredients that can penetrate a bit further into the epidermis, and antioxidants and cell-communicating ingredients that can move deeper yet and influence the development of cells in the healthiest manner possible. When you deliver an abundance of these multifaceted substances to skin it is getting the best the cosmetics industry has to offer.
Which substances can penetrate the skin? That is determined by the molecular weight of the substance. Skin’s barrier (the stratum corneum or corneal layer) is able to defend against the diffusion of many molecules, but not the ones that are small enough to pass through its otherwise impenetrable layers. This is referred to as the Dalton Rule, which set a standard molecular/atomic weight for any given substance. Larger molecules measuring over 500 Dalton cannot pass the stratum corneum, but if they’re under 500 Dalton they sail through. An example of a substance that can sail through the skin is nicotine, as in nicotine patches. In contrast, insulin’s Dalton weight is so high that cannot be absorbed into skin at all, thus diabetics must obtain insulin via shots rather than just sticking a patch on skin.
(Sources: Journal of Biomechanics, April 2008, pages 788-796; Journal of Cosmetic Dermatology, June 2007, pages 75-82; and Skin Pharmacology and Skin Physiology, February 2006, pages 106-121.)