Hand Washing Dishes Trumps the Dishwasher
In spite of what you might have been told by your parents about cleanliness being a supreme virtue, science lately has been revealing reasons to dial down the fastidious. It turns out that if you have kids, too much cleanliness leads not necessarily to godliness, but perhaps instead to asthma, allergies, and increased vulnerability to illness.
Spurred on by recent studies showing that kids brought up in ultra-hygienic homes seem to develop an excess of health problems, scientists have been investigating what they call "the hygiene hypothesis" --the idea that babies need to be exposed to germs in order to develop immunity to them.1 As Dr. David Rosenstreich of the Albert Einstein College of Medicine and Montefiore Medical Center explains, "The whole idea is that humans and all mammals live in homeostasis with all their bacteria in their lungs, skin and GI tract. Having a lot of different bacteria growing inside you tends to stimulate the immune system and makes things stronger."
The hygiene hypothesis has been supported by research showing that early exposure to pets may protect against allergies, as we described in a previous blog post. Other past research found that when parents suck their baby's pacifier and then pass it to the kid, they help build up that baby's resistance to allergies by exposing them to whatever germs lurk in the parental mouth.2 We also know that exposure to bacteria in vaginal birth (as opposed to Caesarian) and breast feeding likewise help train the immune system. Now, new research indicates that children reared in homes where dishes get washed by hand instead of sanitized in the dishwasher have more resistance to allergies. The scientists attribute this result to the fact that dishwashers use stronger detergents and hotter water than hand washing, getting rid of more germs.
The new study, published in the journal Pediatrics, was based on surveys of over 1000 Swedish children aged seven to eight. The researchers found eczema present in 38 percent of children who came from homes using dishwashers, versus only 23 percent in homes where dishes got hand washed. Likewise, in the dishwasher homes, 7.3 percent of children had developed asthma, versus only 1.7 percent in homes using the old-fashioned hand-wash method. In other words, dishwashers were associated with a more than 400-percent increase in asthma cases compared to hand-washing. The results were a bit less startling, but still present, for hay fever cases, with 10 percent of kids from handwashing homes having developed rhinoconjunctivitis compared to 13 percent from homes using a dishwasher.
Not surprisingly, the researchers also found lower allergy rates among those children who ate fermented foods, like sauerkraut and pickles, as well as those who ate food fresh from the farm rather than from the supermarket. Again, fermented foods are awash in beneficial bacteria and farm-grown food, at least theoretically, hasn't been prewashed, homogenized, or sanitized the way store goods often are.
The study certainly delivers a blow to dishwasher manufacturers, who have in the past won almost every showdown when their products are compared to hand washing--but perhaps based on the wrong standards. What are those standards? First of all, dishwashers are easier to use and less messy than hand washing.3 They get dishes cleaner with less effort. According to the folks at Energy Star, using the machine saves about 230 hours of personal time annually that could be used for more entertaining activities.4 Energy Star also claims that dishwashers save the consumer an average of $40 a year in electricity costs compared to hand washing, use 5000 fewer gallons of water, and thus reduce greenhouse gases and pollution. Several non-industry studies support these claims of dishwasher superiority, too.5
However, in spite of whatever advantages machines may confer, if they get the plates and forks just too clean to be healthy, do they need to be used less often? Do the manufacturers need to go back to the lab to develop the "not-so-clean" machine? Even more importantly, are the scientists correct about the hygiene theory, and is the hygiene theory really the explanation for the allergy increase among kids raised in homes with dishwashers?
Certainly, other factors could be at play. For instance, cockroaches and other bugs often sneak into dishwasher tubs, getting easy access to food scraps while hiding from human sight. It's possible that some kids form allergies in reaction to the presence of these bugs, since cockroach allergy is surprisingly common. Then, there's the fact that many people load plastics into their machines, and perhaps exposure to high heat allows plastic chemicals to leach onto dishes-and perhaps these chemicals somehow compromise immune systems. Or perhaps kids in homes without dishwashers typically have had fewer vaccines, and so their immune systems are more active.
In any event, if you must use a dishwasher, you can take comfort in knowing that, according to the Environmental Working Group (EWG), dishwasher soaps typically get slightly higher ratings for safety than products for washing dishes by hand. In any event, no matter which method you use, do check out the safety of the detergent you employ, try to limit water consumption to be kind to the environment, and don't worry about getting the dishes so clean you can see your reflection in them. Oh, and stop using antibacterial hand soaps. Not only are they unhealthy and help breed super bacteria, but when combined with dishwashers, they may just be killing any chance your child has to actually train a strong immune system.
- 1. Firger, Jessica. "Hand wash your dishes to help protect kids from allergies." 23 February 2015. CBS News. 26 February 2015. http://www.cbsnews.com/news/hand-wash-dinner-plates-to-protect-kids-from-allergies/
- 2. McNamee, David. "Fewer allergies among children from dishwasher-free homes." 23 February 2015. Medical News Today. 28 February 2015. http://www.medicalnewstoday.com/articles/289832.php
- 3. "The Great Dishwasher Debate." Natural Resources Defense Council. 27 February 2015. http://www.nrdc.org/living/stuff/great-dishwasher-debate.asp
- 4. "Dishwasher vs. Hand Washing Dishes." Energy Star. 27 February 2015. https://www.energystar.gov/index.cfm?c=dishwash.pr_handwash_dishwash
- 5. Christie, Sophie. "Dishwasher vs washing up: which is cheaper?" 9 December 2014. The Telegraph. 27 February 2015. http://www.telegraph.co.uk/finance/personalfinance/energy-bills/11250403/Dishwasher-vs-washing-up-which-is-cheaper.html