Dishwashers are a mainstay in many homes, schools, restaurants, and anywhere that serves food. Previously, people had to spend hours washing dishes in the backs of bars and cafes, but now the task can be completed with the press of a button. However, a new study from the University of Zurich found that dishwashers may negatively affect people’s gut health.  Although dishes may look squeaky clean after the rinse cycle, they may be covered in a potentially toxic substance.
Dishwasher rinses can hurt gut health
Dishwashers usually work with a combination of hot water, detergent, and pressure mechanics to remove dirt from the utensils and dishes. When the cycle begins, the machine fills with heated water to loosen and dissolve any food particles and grease. Strong motorized motions wash the soapy water over the dishes. Then the dishwasher drains the water and rinses with fresh, clean water. Finally, comes the drying cycle that circulates hot air over the dishes. But some dishwashers includes another step; they add a rinsing agent to the water during the rinse cycle.
“What’s especially alarming is that in many appliances, there’s no additional wash cycle to remove the remaining rinse aid,” says Cezmi Akdis, University of Zurich professor of experimental allergology and immunology, and leader of the study. “This means that potentially toxic substances remain on the dishes, where they then dry in place.”
So Akdis and his team at the Swiss Institute of Allergy and Asthma Research (SIAF), an associated institute of the University of Zurich, wanted to find out the effects of this substance on gut health. They used human intestinal organoids and intestinal cells on microchips, technology specially made for this research. It resulted in a clump of cells resembling the tissue that lines people’s guts. This tissue, the epithelial barrier, lines the entire intestinal tract and controls what gets absorbed into the body. Damage to this barrier has been linked with many medical issues.
“We assume that defective epithelial barriers play a role in triggering the onset of two billion chronic illnesses,” says Akdis. These include food allergies, cirrhosis of the liver, rheumatoid arthritis, chronic depression, gastritis, obesity, diabetes, multiple sclerosis, autism spectrum disorders, and Alzheimer’s disease.
The most damaging ingredient
During the study, the intestinal epithelial-like cells reacted to many commercial detergents and rinse aids, all diluted and concentrated to imitate the amount found on dishwater-cleaned dishes. In the end, high doses of the rinse agents killed the cells, and low doses made the cells more penetrable. The reaction also included several genes and cells signaling proteins that are involved with triggering inflammation. In a detailed analysis, the inflammatory response became attributed to alcohol ethoxylates, an ingredient in the rinse agent. Moreover, alcohol ethoxylates seemed to have the worst potential effect on gut health and the epithelial barrier.
“The effect that we found could mark the beginning of the destruction of the gut’s epithelial layer and trigger the onset of many chronic diseases,” Akdis says. “It is important to inform the public about this risk, since alcohol ethoxylates seem to be commonly used in commercial dishwashers.” 
“One of the greatest threats to humankind”
Akdis has been an active contributor to the epithelial barrier hypothesis, which suggests that many health issues stem from damage to the tissue lining in the outer body, as well as the lining in the gut and respiratory system. Researchers have developed this hypothesis for over 20 years. Part of Akdis’s contribution includes research into substances that damage epithelial barriers. 
Aside from alcohol ethoxylates, other culprits may include laundry detergents, household cleaners, cigarette smoke, enzymes and emulsifiers used in food production, diesel exhausts, and microplastics. “Next to global warming and viral pandemics such as COVID-19, these harmful substances represent one of the greatest threats to humankind,” says Akdis in a 2021 review.
He advocates for more thorough screenings of chemicals used in day-to-day activities, hoping that would promote the development of safer products. This is especially true for products that can directly affect respiratory and gut health. The epithelial barrier hypothesis theorizes that some people have genes predisposed to barrier damage. This is why these diseases affect certain individuals but not others. Akdis hopes further research would discover the biomarkers for these diseases, and be able to monitor those at risk.
“There is a great need to continue research into the epithelial barrier to advance our understanding of molecular mechanisms and develop new approaches for prevention, early intervention and therapy,” says Akdis. These approaches can include reducing exposure to possibly triggering substances, and changes in lifestyle, diet, and microbiome. 
Keep Reading: 7 Easy Ways to Improve Your Gut Health: Recognize The Signs of an Unhealthy Gut
- “Gut epithelial barrier damage caused by dishwasher detergents and rinse aids.” The Journal of Allergy and Clinical Immunology. Ismail Ogular, PhD, et al. December 1, 2022.
- “Commercial dishwashers destroy protective layer in gut.” Eurekalert. University of Zurich. December 1, 2022
- “The epithelial barrier hypothesis proposes a comprehensive understanding of the origins of allergic and other chronic noncommunicable diseases.” The Journal of Alergy and Clinical Immunology. Cezmi A. Akdis, MD. November 22, 2021
- “Defective epithelial barriers linked to two billion chronic diseases.” Science Daily. University of Zurich. May 6, 2021