Dishwashers are a wonderful modern convenience that shave time off of our regular routine of cleaning up after each meal.  And common sense would dictate that they are probably safer to use than hand washing plates, glasses, cutlery, and all types of cooking utensils since they use extremely hot water and the jets don’t miss many spots.  However, new research, first published in 2011, may call the safety of dishwashers into question, as the findings show that they appear to be a breeding ground for potentially deadly microbes.

The study, which was conducted at the University of Ljubljana, Slovenia, found that dishwashers, and to some extent certain other household appliances, often harbor fungi that can sicken or even kill us.¹ Zalar P, Novak M, de Hoog GS, Gunde-Cimerman N. “Dishwashers–a man-made ecological niche accommodating human opportunistic fungal pathogens.” Fungal Biol. 2011 Oct;115(10):997-1007. http://www.ncbi.nlm.nih.gov/pubmed/21944212   These inlcuded the black yeasts Exophiala dermatitidis and E. phaeomuriformis and one white yeast called Candida parapsilosis, followed by low level occurrences of red yeast Rhodotorulla, as well as the molds Magnusiomyces and Fusarium..  The scientists took samples from the rubber piece in the door of dishwashers in 189 private homes across 102 varied communities.  The majority were from Slovenia, but others came from other parts of Europe, and as far away as North America, South America, Asia, Australia, Israel, and South Africa.

The researchers found that a frightening 62 percent of the dishwashers tested positive for these fungi.  Samples from coffee makers and washing machines also determined the presence of Exophiala dermatitidis and E. phaeomuriformis, but they were not nearly as common within these appliances.  While it is hard to believe that any living organism could possibly survive a dishwasher cycle using intense heat, potent dishwashing detergents, and high levels of salt, the microbes did just that.  The scientists studied the reaction of the fungi to a variety of harsh circumstances including very high temperatures, great concentrations of salt, cleaning agents, and water with an acid pH as well as an alkaline pH.  Both forms of Exophiala withstood all of these elements, which may explain how they can thrive within the dishwashers in so many homes. In fact, both the black yeast Exophiala and the mold Magnusiomyces capitatus thrive in high concentrations of salt, which is often used to soften hard water to avoid the accumulation of calcium  mineral deposits in appliances.

These results were confirmed in a more recent Turkish study published in July of this year. In this study, researchers found that almost one in five dishwashers yielded fungi, of which 86% were the black yeasts, followed by a few white yeast and the mold Magnusiomyces.² Dögen A, Kaplan E, Oksüz Z, Serin MS, Ilkit M, de Hoog GS. “Dishwashers are a major source of human opportunistic yeast-like fungi in indoor environments in Mersin, Turkey.” Med Mycol. 2013 Jul;51(5):493-8. http://www.ncbi.nlm.nih.gov/pubmed/23167707

Exophiala have generally been believed to spread mainly through the air in the form of spores, but these findings suggest that they may be transmitted by our water sources.  Without testing, it is impossible to determine their presence as they are microscopic in size.  And these fungi can prove very dangerous to people, increasing the risk of developing sinus infections, asthma, fatigue, rheumatoid arthritis, and gastrointestinal ailments.  Exophiala is particularly detrimental to the very young, the elderly, and those with diseases such as cystic fibrosis because their immune systems have more trouble fighting off the microbes.  But even healthy individuals have been known to become sickened or even die from recurrent infections with Exophiala.

A 2007 study at the Institute for Biodiversity and Ecosystem Dynamics in Amsterdam, The Netherlands concentrating on various Exophiala species determined that infections with this fungi are grossly underdiagnosed in the United States because doctors are simply not that familiar with them.³ Zeng, J.S.; et al. “Spectrum of Clinically Relevant Exophiala Species in the United States.” Journal of Clinical Microbiology. November 2007. Accessed 8 October 2013. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2168524   It is often difficult to know if you have developed an infection due to these bacteria since they can affect so many parts of the body.  One of the best ways to protect yourself from an infection with Exophiala or many other types of bacteria and fungi is to maximize your health prophylactically and optimize your immune system.  Having a strong immune system will enable you to fight off many invaders that attack from all kinds of sources.  To learn more about how to have a healthy immune system, check out Jon Barron’s special report on Building Your Immune System.

And to prevent these nasty bugs from colonizing your dishwasher and other household appliances, try to clean them thoroughly using a mixture of vinegar and baking soda.⁴ Martin, Laura J. “Day2Night: How Mom Can Stop Germs.” WebMD. 5 December 2011. Accessed 8 October 2013. http://www.webmd.com/parenting/d2n-stopping-germs-12/kitchen-germs?page=1   After the rubber parts of the dishwasher have been scoured with this cleanser, run an empty cycle with vinegar rather than dishwashing detergent.  Repeat this cleaning process every few months to discourage the recurrence of Exophiala colonies. A simpler but more expensive solution is a product called Smelly Washer 216 Dishwasher and Disposal Cleaner. They also make a version for washing machines.⁵ http://smellywasher.com