Approximately 54% of households in the U.S. have dishwashers and use them at least once per week 1. What many families don’t understand is that dishwashers can be breeding grounds for dangerous bacteria and fungi, so are dishes actually cleaner after going through the dishwasher?
A recent dishwasher study conducted at the University of Ljubljana in Slovenia and the University of Copenhagen in Denmark has shown dishwashers contain bacteria that are linked to urinary tract infections, skin infections, food poisoning, and heart infections. It also uncovered that fungi thrive in many dishwashers and can cause yeast infections and thrush 2. Approximately 309 distinct bacteria OTUs (operational taxonomic units) and 194 unique fungal OTUs were found living in the 24 sampled household dishwashers.
With these harmful organisms lurking inside household dishwashers, you might be wondering if your dishwasher is safe to use and how you can prevent your family from becoming sick from these nasty bugs.
First, we’ll go over some dish washing basics, and then we will discuss how you can reduce your family’s exposure to these critters.
Why do people buy and use dishwashers?
People purchase dishwashers because they want to spend less time doing dishes and to make their dishes sanitary–especially after handling raw meats and other foods that can contain harmful bacteria and viruses. Higher washing temperatures found in dishwashers make homeowners believe that when they use their dishwashers that their dishes come out cleaner and safer than they would if they had been hand washed. However, this is not always the case.
What are the different kinds of dishwashers?
What many people do not understand is that not all dishwashers are created equal. Some dishwashers can sanitize dishes while others cannot. Here’s a simple breakdown of the differences:
- Standard Dishwashers — common household dishwashers that do not have a hot enough or long enough rinse cycle to kill most harmful bacteria
- Sanitizing Dishwashers — sanitizing dishwashers are often NSF (National Science Foundation) certified. NSF certified dishwashers must reach a minimum final rinse temperature of 150ºF and achieve a minimum 99.999% reduction of bacteria 5
If your dishwasher is not NSF certified, it’s probably less effective at killing the microorganisms in your dishwasher and on your dishes.
What kinds of bacteria and fungi are commonly found in dishwashers?
The types of bacteria and fungi sampled in the study varied across households. “The age, usage frequency, and hardness of incoming tap water to the dishwashers had significant impact on bacterial and fungal community compositions 3.” Of the many bacteria and fungi that were sampled, the following were most prominent in the dishwashers:
Bacteria:
- Psuedomona — a type of bacteria that is abundant throughout the world and can cause a variety of health issues depending on the location of the infection. However, it usually only poses a major risk of infection to those who have a compromised immune system 6.
- Escherichia — a type of bacteria that is commonly found in the gut lining of humans and warm-blooded animals. Some types of Escherichia are human pathogens (like E. Coli) and can be the most common cause of urinary tract infections, gastrointestinal disease, and female reproductive issues 7.
- Acinetobacter — is a bacteria that frequently causes pneumonia, urinary tract infections, and meningitis. This bacteria is especially prevalent in hospitals and intensive care units (ICUs) 8.
Fungi:
- Candida — a type a yeast that normally lives in small amounts in places like your mouth, stomach, and skin. However, when environmental conditions are right, it can multiply rapidly and cause yeast infections and thrush9.
- Cryptococcus — a fungus that is commonly found in soil contaminated by bird droppings or in decaying wood. Inhalation of it can cause cryptococcal meningitis, which is a terrible and sometimes fatal infection. People who have compromised immune systems are more susceptible to this fungus 10.
- Rhodotorula — an opportunistic pathogen with the ability to cause bloodstream infections in people who have compromised immune systems. It has a higher prevalence in hospitals with most infections stemming from usage of central venous catheters or people who have undergone an organ transplant or chemotherapy 11.
These potentially dangerous organisms that inhabit household dishwashers present a disturbing challenge for homeowners.
How can you better contain these bacteria and fungi to reduce your risk of exposure to them?
1. Use soft, filtered water to wash your dishes. Hard water increases the prevalence of dishwasher fungi because it has minerals that these organisms adhere to 3. Hard water can also cause cloudiness and filming on your dishes; these films can be a breeding ground for bacteria and other organisms–even after your dishwasher has finished its washing cycle. However, when soft, filtered water is used, it makes it easier for your dishwasher to do its job. Softened water helps to more fully clean your dishes, and it reduces the annoyance of water spots on your glasses and silverware so that you can feel more confident that you are eating off of cleaner dishes.
2. Clean your dishwasher monthly with a vinegar rinse. Vinegar is a natural, biodegradable acid that kills some bacteria and viruses 12. It also helps get rid of grease and odors in dishwashers. To clean your empty dishwasher, place a cup of white vinegar on the top rack in an open, dishwasher-safe container, and run the machine through a hot water cycle 4.
3. Clean the seal of your dishwasher weekly with a 10 percent bleach to water solution. To make this solution, mix 9 parts water to 1 part bleach. You can also use this solution to clean the bottom and sides of your dishwasher to help prevent buildup of debris 4.
4. Don’t open your dishwasher while it’s still hot. The bacteria can become airborne through the steam if you open the dishwasher before it has cooled down 13.
