Unexpected: The most innocent places in the house that hide a world of bacteria

We wash the bathtub, clean the toilet, and change the sheets, but there are places in the house that most of us hardly think need cleaning. Studies conducted in recent years show that bacteria and fungi can establish themselves even inside the shower head, bath toys, the dishwasher, and the toothbrush holder. This does not mean that the house is dangerous or that you need to disinfect everything you touch, but the findings reveal how misleading our definition of "clean" can be.

Shower head: What is hiding in the place where the water comes out?

This is probably one of the last places we would think of. We stand under the shower head to get clean, but inside the device itself, a layer known as biofilm can develop – a kind of community of microorganisms that attaches to the surface.

Researchers from the University of Colorado Boulder and other institutions tested samples from shower heads in 656 households in the United States and Europe. In the study, published in the scientific journal mBio, it turned out that mycobacteria were on average the most common group of bacteria in the biofilm tested. The researchers also found large differences between regions and types of water systems. It is important to emphasize that not all mycobacteria are dangerous, and the mere fact of finding them in a shower head does not indicate that someone showering under it will get sick.

So what to do? It is recommended to clean the shower head from time to time and remove limescale and accumulations according to the manufacturer's instructions. If it can be disassembled, you can also clean the accessible internal parts. It is advisable to avoid mixing different cleaning agents.

Rubber duck: The surprise is actually inside

It looks completely innocent and floats in the water where children bathe, but the inside of hollow bath toys can become an especially comfortable environment for microorganisms. Researchers from the Swiss Federal Institute of Aquatic Science and Technology (Eawag) and the Swiss Federal Institute of Technology (ETH) Zurich tested 19 bath toys that were exposed to real conditions. In all the toys tested, biofilms were found on the internal surfaces, and in 58% of them, fungi were also found.

The reason is related, among other things, to the water that enters through the hole at the bottom of the toy and remains inside. Together with substances from bathing products and the body, conditions are created in which microorganisms can develop. This is also the reason why sometimes, when you press on an old bath toy, cloudy water or a dark substance comes out of it.

So what to do? It is advisable to empty the water from the toys after each use and allow them to dry completely. You can also choose toys that are not hollow or those that can be opened and cleaned from the inside. If dirt has accumulated inside a toy that cannot be removed, replacing it may be the simplest option.

Toothbrush holder: The innocent cup that almost no one cleans

We are careful to change our toothbrush, but what about the place where it stands? In a home study by NSF International, samples were taken from objects and surfaces in homes. One of the surprising results concerned the toothbrush holder: coliform bacteria were found in 27% of the holders tested. Water from the toothbrush drips to the bottom of the holder, and without cleaning and drying, moisture and residues can accumulate there over time.

So what to do? NSF recommends cleaning the holder once or twice a week. If it is dishwasher safe, it can be washed there, and if not – wash with hot water and soap and dry thoroughly.

Dishwasher: Even the device that cleans the plates is not sterile

The dishwasher seems like an especially hostile environment for bacteria: hot water, detergents, and repeated rinse cycles. And yet, it turns out that some microorganisms manage to find a place to live in it. A study published in BMC Microbiology tested rubber seals from 30 home dishwashers. The researchers found bacteria in all the dishwashers tested and isolated hundreds of samples belonging to dozens of species.

Other studies have also found fungi and bacteria in biofilms that formed on the seals. These areas are particularly interesting because they do not necessarily go through the same cleaning process as the dishes themselves.

So what to do? It is recommended to remove food residues, clean the filter according to the manufacturer's instructions, and wipe the seals and grooves from time to time. Here too, it is important to use only cleaning agents suitable for the device and not to mix substances.

Washing machine: It cleans the clothes – but who cleans it?

The fact that the clothes come out clean does not mean that the washing machine itself is sterile. Water can remain in the rubber seals and other parts of the machine, especially in front-loading machines. A combination of moisture, detergent residues, and organic matter can create conditions in which microorganisms survive. This is especially prominent in an era where a large part of the laundry is done at relatively low temperatures. However, the presence of microorganisms in the machine does not mean that the clothes coming out of it are dangerous.

So what to do? It is recommended to leave the machine door open after washing to allow the internal parts to dry, clean the rubber seal and the detergent drawer, and run the machine's cleaning program according to the manufacturer's instructions.

Coffee machine: The damp place we forget about

Another place that many do not think about is the water reservoir of the coffee machine. In the home check by NSF International, the coffee machine reservoir was found among the places where microorganisms were detected. The damp environment and the fact that the reservoir is not always washed and dried completely make it a place that should be included in the cleaning routine.

So what to do? It is not advisable to leave standing water in the reservoir for a long time. Removable parts should be washed and dried, and cleaning and descaling should be performed according to the machine manufacturer's instructions.

Many of these places have a common denominator: moisture. A shower head, a bath toy, a washing machine seal, and a coffee machine water reservoir can remain wet for hours – and sometimes almost continuously. When moisture is joined by a suitable surface and substances that microorganisms can use, a biofilm may form. Therefore, a place does not have to look dirty for bacteria to live in it.