Detergents Disrupt Body Barriers
I will not apologize for my nerdiness here—I am really excited about a recent study exposing the damaging effects of detergents on the skin barrier, as well as the causal role detergents likely play in the development of eczema, food allergies, asthma, and autoimmune disorders, among other diseases.
Not because this is a new concept, but because one of the authors is Dr. Kari Nadeau, a world-renowned expert in pediatric food allergies and asthma. I can name about three “famous” allergists in the world, and she is one of them. In other words, this study and accompanying paper bring significant credibility to the topic of detergents and skin barrier integrity!
In fact, Dr. Nadeau has a number of recent publications in this space, all touching on the “epithelial barrier hypothesis.” In short, this hypothesis links the steep rise in allergic and autoimmune diseases (among others) to environmental agents that disrupt epithelial barriers, such as the barriers of the skin, gut, and lungs [1]. Those environmental exposures include—you guessed it—synthetic detergents and surfactants.
Let’s take a look at the study, and then I’ll share my two cents on how this area of research is evolving.
The Study
The study is: Arturo Rinaldi et al., Household laundry detergents disrupt barrier integrity and induce inflammation in mouse and human skin, 79 Allergy 128 (2023) [2]. Linked here.
This study finds that laundry detergent residue in clothing—even at the small doses remaining after a complete wash and rinse cycle—impairs the integrity of the skin barrier. In other words (my own), detergents make the skin more permeable—allowing things that should stay in (like moisture) to come out, and allowing things that should stay out (like allergens, bacteria, and chemicals) to come in.
This is important, because a defective barrier is believed to contribute to the development of eczema and food allergies, among many other diseases.
In short, according to this study, daily exposure to detergents may impair the skin barrier, lead to allergen sensitization, and contribute to other allergic diseases.
Healthy skin barrier vs. damaged skin barrier. Image from the National Eczema Association, nationaleczema.org/blog/what-is-my-skin-barrier.
Turning to the details, this study examined two different household detergents, each containing a combination of dozens of different chemicals, as well as one synthetic surfactant in isolation—sodium dodecyl sulfate (i.e. SDS, sodium lauryl sulfate, or SLS).
Both of the detergent samples, as well as SDS/SLS in isolation, were found to impair the skin barrier in a mouse model and in an ex vivo human skin biopsy. “Detergent B,” which contained a higher concentration of synthetic surfactant, had a more damaging effect in the mouse model and was used for the testing on human skin.
The graphs below show the impact of Detergent B and SDS/SLS on ex vivo human skin at various levels of dilution. The EIS (electric impedance spectroscopy) measurement reflects skin barrier function, with a higher number indicating a stronger barrier function, and a drop in EIS indicating a weakening of the skin barrier. “PBS,” or phosphate-buffered saline, was used as a control.
As shown here, at the 6-hour mark, there is a statistically significant decrease in skin barrier function for all four levels of dilution of the detergent and SDS/SLS (as compared to the PBS control).
Then something noteworthy happened at the 6-hour mark: the detergent and SDS/SLS were washed off of the skin samples. So while the skin barrier function measurements appear to somewhat stabilize after the 6-hour mark, that recovery occurred only after the detergent exposure ended.
Notably, the detergent dilution rates used in this study reflect the amount of detergent residue that likely remains on clothing after a full wash cycle. This study suggests that a ratio of 1:2,500 is a reasonable estimate for detergent residue on clothing after a machine wash, and that a ratio of 1:400 is a reasonable estimate for hand washing. As shown in these results, a more concentrated detergent solution (such as with handwashing, or using a large amount of detergent in a machine wash) causes more damage to the skin barrier.
In addition to the EIS scores, this study also found that the household detergents substantially reduced the expression of multiple genes essential for skin barrier integrity.
This study theorizes that prolonged exposure to detergent residue—even at low doses—on a daily basis may progressively impair the skin barrier, exacerbating eczema and increasing risk of allergen sensitization. Household cleaning products, toothpastes, and dishwasher detergents are also called out as potential problems for epithelial barriers.
The authors acknowledge a few limitations of this study. First, this study shows a one-time stimulation. The detergent and SDS were applied to skin samples for 6 hours, and then washed out with PBS three times. In reality, our skin is constantly in contact with our clothes, and therefore constantly in contact with detergent residue. This study does not reflect that nearly perpetual exposure. Second, no components other than SDS/SLS were studied in isolation (laundry detergents contain dozens of chemicals other than surfactants that might also impact skin health). Third—and most unfortunately from my perspective—a true soap was not studied as a comparison. Hopefully these are subjects for future research.
Recent Study, Not a Recent Concept
As I noted at the outset, this theory—that detergents damage the barriers of the skin, lungs, and gut (as well as other tissues), and that this contributes to the development of eczema, food allergies, asthma, and autoimmune disorders, as well as autism, Alzheimer’s disease, and depression, among other diseases—is not a new one.
Earlier sources explicitly posited a similar theory at least as early as 2004 [3]. Even Dr. Nadeau has suggested reducing detergent exposure as an allergy prevention strategy for several years now [4].
So if this is not a new theory, why is it gaining momentum now?
My take on this question is that a couple of different puzzle pieces are now coming together in a convincing manner—the first puzzle piece being the causal connection between barrier disfunction and disease, and the second puzzle piece being the causal connection between detergents (and other chemicals) and barrier disfunction.
Regarding the first puzzle piece, barrier disfunction is widely believed to be implicated in numerous chronic diseases. When my son was young, we saw countless dermatologists and allergists, and all of them spoke in terms of skin barrier disfunction. Eczema is described as a skin barrier defect, and that defective skin barrier is believed to contribute to the development of food allergies. In short, when an infant has a defective skin barrier, food proteins are able to enter the body through the skin barrier, which is thought to increase the risk of the immune system labeling the food protein as a threat, and then later, when that food is ingested, launching an allergic reaction.
Intestinal barrier disfunction—or a “leaky gut”—was once dismissed as quackery, but is now widely believed to be implicated in intestinal diseases like IBS, as well as neurological conditions like Alzheimer’s disease. In fact, my sister who is studying to become a nurse anesthetist recently wrote a paper on the causal connection between intestinal barrier disfunction and Alzheimer’s—in short, the theory is that a leaky gut allows inflammatory molecules to cross the intestinal barrier, travel to the central nervous system, and then cross the blood-brain barrier where they cause brain inflammation associated with Alzheimer’s.
Regarding the second puzzle piece—detergents causing barrier disfunction—I began noticing breadcrumbs of big names (Yale, Stanford, etc.) researching this topic in earnest in early 2021. Since then, there have been numerous papers—authored by big names like Dr. Nadeau—linking synthetic detergents and surfactants to barrier disfunction of the skin, lungs, gut, and other tissues.
Today, the combination of these two puzzle pieces has a name: the Epithelial Barrier Hypothesis. With big names—and hopefully big money—taking interest in this area of research, there is sure to be more to come.
Sources
[1] Cezmi Akdis, Does the epithelial barrier hypothesis explain the rise in allergy, autoimmunity and other chronic conditions? 21 Nat. Rev. Immunol. 739 (2021). See also Cezmi Akdis, The epithelial barrier hypothesis proposes a comprehensive understanding of the origins of allergic and other chronic noncommunicable diseases, 149 J. Allergy Clin. Immunol. 41 (2021).
[2] Arturo Rinaldi et al., Household laundry detergents disrupt barrier integrity and induce inflammation in mouse and human skin, 79 Allergy 128 (2023).
[3] A.J. Lumsdaine, Eczema: One Family’s Solution, http://solveeczema.org. See also A.J. Lumsdaine & J.C. Ross, Abnormal Amplification? Observations from Applying the Engineering Method to Solving Eczema and Atopic Disease, The Winnower (2017), available here.
[4] See, e.g., Kari Nadeau, Let’s Focus on Food Allergy Prevention, TEDx Palo Alto (June 6, 2018), https://www.youtube.com/watch?v=Gv17TWhDjgw (talking about the 6 Ds to decrease the risk of food allergy: Dirt exposure, Dry skin care, Diet diversity early, Vitamin D levels, Dog exposure, and less Detergents).
