Skin Absorptivity - What ingredients in our lotions stay at the surface and what ingredients get absorbed?

Our skin forms a protective barrier to the outside world, so we think of our skin as impermeable.  But the truth is, our skin is selectively permeable.  This term means that some small molecules pass through our skin.  For example, absorption through our skin is a drug delivery method used by the nicotine patch.  The drug in the patch is a small molecule that is absorbed through all the layers of skin cells and makes it into our blood stream.  Some hormones and pain medications are also delivered in this way. 

Most components in lotions work at the surface to from a moisture barrier.  If molecules are absorbed through the skin, they are thought to mainly work in the outer-most layers of our skin, but not make it into our bloodstream.  However, some carbon-based sunscreens were found to make it all the way into our bloodstream.  This is worrisome because these ingredients were only approved by the FDA to be safe for external use.  The FDA approval process for synthetic food ingredients or medicines is very different and much more extensive than the approval process for ingredients in personal care products like lotions. 

CNN covered this important study published in JAMA, the Journal of the American Medical Association. This study showed that carbon-based sunscreens (oxybenzone, avobenzone, and others) are absorbed through the skin and are found in the bloodstream after just one day of use. 

https://www.cnn.com/2019/05/06/health/sunscreen-bloodstream-fda-study/index.html

https://www.cnn.com/2020/01/21/health/sunscreen-dangers-chemicals-bloodstream-wellness/index.html

We can make predictions about what can be absorbed through the skin by determining what compounds can cross membranes.  Biochemists have studied membrane permeability extensively and found that small, oil-loving compounds can cross cell membranes easily while water-loving molecules are must less likely to cross.  Some water-loving molecules, like sugars and other nutrients have special transport mechanisms in our digestive system to bring them into the bloodstream, but these transport mechanisms are not all present in our skin cells.  We can determine which molecules are water-loving and which are oil-loving by stirring them in both oil and water and seeing which substance they mix with most easily.  For example, sugar dissolves in water, so is water-loving and requires help crossing a cell membrane.

Carbon-based sunscreens are oil-loving, and were found to make it into our bloodstream.  What other components of lotions are small oil-loving molecules?  Parabens and phenoxyethanol are present in many personal care products like lotions to give them a long shelf life.  Studies are still underway to determine if these ingredients are safe inside our bodies. The Environmental Working Group, http://www.ewg.org, is a good place to stay up to date on these studies.

Vitamin E is also oil-loving and likely to be absorbed, but it is also present and safe in food. Small, oil-loving molecules that have already been approved by the FDA for food products are likely also safe in personal care products.  Avaisn chooses food-safe ingredients in our products to ensure product safety.