Dishwashers run on hot water and detergent, so it is easy to assume their interiors stay clean. But studies have found that bacteria and mold can live in parts that are hard to reach, such as rubber door seals and filters.
A study published recently in the Brazilian Journal of Microbiology found several types of mold in 22 household dishwashers examined by researchers at the University of Wroclaw in Poland.
Mold turned up most often in the rubber seal along the edge of the dishwasher door. Moisture and food residue collect easily there, creating conditions where microorganisms can take hold.
The most common find was Exophiala dermatitidis, a type of black yeast. Several other fungi, including Candida species, were also detected. Most do not immediately cause illness in healthy people, but the group included microorganisms capable of causing infections in people with severely weakened immune systems.
Bacteria can also be found in dishwashers. A study in the latest issue of BMC Microbiology examined the rubber seals of 30 household dishwashers and detected bacteria in every one. The researchers said microorganisms carried in on food-covered plates and cooking utensils can remain on the rubber seals and elsewhere.
That does not mean dishes come out of a dishwasher covered in bacteria. The studies found microorganisms mainly in specific spots inside the machine, such as the rubber seals.
The point is that dishwashers themselves need regular cleaning. Washing dishes with hot water and detergent does not clean the inside of the machine on its own.
Filters and drains, where food residue tends to gather, should be cleaned regularly, and the rubber seal along the door edge should be wiped down. It also helps to keep food residue and moisture from sitting inside the dishwasher for long periods.
