Skin absorbs 70% of everything you put on it.....or does it?

You only have to search the internet for bold claims that our skin absorbs 70% of everything that we put on it. Or the fanciful claims that our skin is like a sponge.  Now as with all urban myths sometimes there is an element of truth to them.  Whilst the skin can absorb a small amount it is a formidable barrier to most compounds.  It is designed to keep out the environment and to protect us.

There are thousands of alarmists who have blogs on the internet that sprout incorrect information surrounding chemicals, toxicity and absorption.  Read any of these blogs and you will find claims that our bodies absorb X amount of cosmetics every year.  Others will cite that there are chemicals found in urine which implies that the chemicals presence is a danger to us and our health.  The presence of a chemical in our urine doesn't imply actually anything.  The chemical may have no effects at all in the body and may simply be excreted unchanged, or it may have a biological influence and effect.

There are also a number of physiological factors that affect the skin barrier and hence skin permeability:

Everything is a Risk, but Not Necessarily a Harm

When a chemical penetrates our skin and is absorbed into our bodies, is may be converted into another chemical form, metabolized or accumulate.  Absorption into the body doesn’t equate to bodily harm.  What happens after a chemical is absorbed makes the distinction!  Our bodies design will filter out molecules and water, disposing of what doesn’t belong by excretion via bodily fluids.

Points that need to be considered when examining studies on cosmetic ingredients are the following:

• How long were the test subjects exposed to the chemical?
• What was the method of absorption?  Was it topical, oral or injection?
• What is the molecular size of the molecule?
• What does the ingredient respond after it is absorbed?

These points are crucial to examine.  Citing a study where a rat was fed a chemical is not a "real life" scenario.  Most people don't drink their cosmetics.  It is increasingly being found that  animal research may be a poor predictor of a chemicals effects on humans.   Pharmacologists, in particular, have long recognized the difficulties inherent in extrapolating drug data from animals to man.   You only have to examine the literature to find fault with animal tests.  Roaccuatane for example causes birth defects in rabbits and monkeys as well as in humans, but not in mice or rats. [1].  By contrast, corticosteroids are widely teratogenic in animals but not in humans [2], and thalidomide is not a teratogen in many animal species but it is in humans [3]
Determining the safety of a chemical in skin absorption is about risk assessment.  The toxicity of an ingredient is in the amount absorbed and accumulated, or “the dose makes the poison.”  As a species we require Oxygen at 21% in the atmosphere.  100% oxygen will kill us.  Now that doesn't make oxygen evil or toxic.  It simply means there is a correct amount that is not toxic.  The same applies with water.  We need it to live or we will become dehydrated, however the same compound can kill us by drowning.

But what about garlic being rubbed on the feet?  There is many a misinformed alarmist that will tell you that because garlic can be tasted in your mouth from rubbing it on your foot, that this indeed is PROOF that what we put on our skin gets absorbed into our bloodstream.

Here comes the enlightenment......

Smell and taste are part of the same interconnected sensory system.  The flavor of food is almost entirely detected in the nose and not the tongue. The taste receptors on the tongue and the "oderant" receptors in the nose work together to tell us about the air we breathe and the food we eat.  So you are actually not tasting it but your nose detects the scent and therefore it registers in the brain and you "taste it".  This is why when garlic is rubbed on the soles of the feet that you taste it.  It isn't because the garlic has penetrated the skin and somehow absorbed into our bloodstream as the toxic alarmists would have us believe.

The distinction between penetration and absorption is a crucial one where measurement of chemical risk is concerned.  Skin Penetration means that it is absorbed into the top layers of the skin and doesn't affect body systems.  Skin Absorption occurs when it breaches the skin barrier and reaches the blood stream.  Our bodies have amazing receptors called Aryl hydrocarbon receptors that filter out chemicals via bodily fluids.

So coming back to the original question of does our skin absorb 70% of everything that we put on it?  The answer is NO.

So where did this information come from?

The quote of 70% comes from a journal paper titled "The Role of Skin Absorption as a route of exposure for Volatile Organic Compounds in Drinking Water".

The answer:

Ethylbenzene

Toluene

Styrene

These are solvents that may be found at extremely low concentrations in drinking water – the focus of the study. None of these solvents are used in skin care cosmetics. Toluene is only used in some nail products, with an extremely low risk of skin penetration.

To compare a study that uses chemicals that are not even used in cosmetics is hardly scientific or fair to the cosmetic industry.

References:

Nau H (2001). Teratogenicity of isotretinoin revisited: species variation and the role of all-trans-retinoic acid. Journal of the American Academy of Dermatology 45:S183-7.

Needs CJ, Brooks PM (1985). Antirheumatic medication in pregnancy. British Journal of Rheumatology 24:282-90

Lepper ER, Smith NF, Cox MC, Scripture CD, Figg WD (2006). Thalidomide metabolism and hydrolysis: mechanisms and implications. Current Drug Metabolism 7:677-85

Brown, H; Bishop, D and Rowan, C. "The role of skin absorption as a route of exposure for volatile organic compounds (VOCs) in drinking water". Am J Public Health. 1984 May; 74(5): 479–484.