Over the past twenty years, more than 10,000 Americans have had their blood tested by the U.S. Centers for Disease Control and Prevention (CDC) in an attempt to determine their “chemical body burden.” The results of the CDC study were stunning: even those who lived in remote areas were found to have hundreds of synthetic chemicals in their bloodstream(1). More disturbingly, this chemical exposure begins even before we take our first breath— an astounding 287 chemical toxins have been detected within the umbilical cord blood of newborns(2)
So how do these harmful synthetic chemicals get into our (and our children’s) bloodstream, and where do they come from? If you’re aware of the issue, you might not be surprised to hear that some of the toxic chemicals detected in the bodies of those tested are common ingredients in mainstream personal care products. As the public becomes increasingly aware of the harmful chemicals found in skin care and cosmetics, claims that toxic chemicals from these products can enter our bodies through the skin have become commonplace. Statistics like “your skin absorbs 60% of what you put on it,” and “anything you put on your skin is absorbed into your bloodstream within 26 seconds,” pop up frequently across the internet in forums, blog posts, infographics and even company websites(3). On the other hand, there are many people who declare the skin to be an absolutely impenetrable barrier— one that does not allow substances to penetrate even the uppermost layers, let alone the lower layers of the skin where the blood vessels are.
Is either side correct? And if not through the skin, can chemicals from our personal care products enter our bodies through other means? Let’s take a look.
Multiple factors: Skin anatomy and chemical structure
One of the many functions of the skin is, indeed, to be a barrier: it keeps our internal organs and fluids in, and harmful external elements (UV radiation, bacteria) out. The skin can be divided into three distinct parts: the epidermis, the dermis, and the hypodermis. The epidermis is comprised of five layers of dermal cells, the uppermost layer (the stratum corneum) being our first line of defense against the outside world. The stratum corneum is a sheath of flattened, dead skin cells surrounded by water-repelling lipids— this explains why our bodies don’t swell up like a sponge every time we take a bath.
Though these outer layers of skin do a good job at keeping elements like water from seeping in, absorption of certain chemicals through the skin is very real. Many medicines are delivered through the skin, most often in the form of patches or gels. This method is quite potent and effective at delivering chemicals into our body-it’s even possible to die from an overdose on a fentanyl patch(4).
The ease at which substances are absorbed into our skin depends on a number of factors, including the structure and size of the chemical applied to the skin. While a lot of chemicals are simply too big to be absorbed by the skin, others are just small enough. Some are even designed to penetrate the skin quickly and easily, like nanoparticles and “penetration enhancers” found in many lotions and sunscreens.
Absorption of chemicals into the skin also depends on other factors, like skin integrity (damaged vs. intact), skin temperature, concentration of a chemical on the skin surface, length of time exposed, and perhaps most importantly, the area of your body exposed. Skin absorption rates vary greatly among different parts of the body; for example, the chemical absorption rate on your forehead and scalp is about four times greater than the absorption rate on your forearms(5).
So the answer to a question like “how much does the skin absorb?” cannot possibly be quantified in a single, universal percentage— it depends on a significant number of complex, situationally-contingent variables.
“Dermal Absorption”: the three ways chemicals enter the skin
Generally speaking, there are three different routes through which a chemical can enter the skin: intracellular, intercellular, and transappendageal.
Chemicals can penetrate the skin by passing directly through cells via permeation (intracellular), weaving their way between cells (intercellular), or by sneaking in through appendages like hair follicles or sweat ducts (transappendageal). If a chemical successfully passes through the upper layers of skin, it has the chance to be absorbed by the bloodstream or lymphatic system(6).
Harmful chemicals in personal care products can enter our bodies through non-dermal pathways as well. Some of the most worrisome toxics are phthalates, which are often found in the ingredient “parfum” or “fragrance.” Phthalates can end up airborne, entering into our system through inhalation, depositing in airways, and being absorbed into the bloodstream through the lungs.
Skin care and cosmetic products can also be ingested. For years, studies have been finding heavy metals, like lead, in lipsticks and other lip products. People who reapply lip products several times a day can ingest a significant amount of these ingredients, even surpassing the daily recommended exposure to some heavy metals(7). It’s also possible to accidentally ingest facial products we apply close to our mouths, as well as products like shampoos and conditioners which often run down our faces while we’re in the shower.
It is clear that the skin is not the impenetrable barrier that some claim it to be, although the factors that affect dermal absorption are so complex that knowing exactly how much of which chemical is being absorbed is impossible. Yet this “unknowability” is perhaps more concerning than an unchanging statistic. Add to this the fact that we can inhale and ingest ingredients in products, and it seems pretty likely that some harmful chemicals from personal care products do eventually enter our bloodstreams. While it might not be a huge amount (like 60%, as some would have you believe), a growing body of research is showing that even minute amounts of chemicals, when combined with other chemicals, can have unpredictable effects on the body ( LA Times).
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