Most everyday objects are at least a little bit grimy. They rarely, if ever, make contact with soap or disinfectant – unlike your toilet seat, even though that’s the one that’s often used as a symbol of filth in studies of household cleanliness. Aside from pathogens that can cause disease and illness, “for the most part, we’re dealing with our own bacteria”, says Jason Tetro, microbiologist and author of The Germ Code. This usually isn’t a problem, especially for youngish healthy people – but, Tetro adds, “when they accumulate, even if they are your own, it can lead to things like skin irritability, itchy scalp, cavities [in teeth from bacteria-heavy toothbrushes], that type of thing”.
Does it matter that your reusable shopping bag might be carrying faecal bugs? Or that your watch strap is teeming with lifeforms? Are the studies – usually small, and sometimes conducted by cleaning-product companies – scaremongering or a grave matter of public health? Germ experts come clean.
Your taps
After going to the loo, or every time your hands are dirty, you touch the tap before washing them. “If you don’t have those [long lever] elbow taps like they have in hospitals, then you’re going to be making your taps really gunky, and lead to the potential for cross-contamination,” says Tetro.
Clean bathroom and kitchen taps regularly. In the kitchen, if you’re washing your hands after handling raw meat, consider turning the tap on before you start. “I would suggest you just keep a little stream going, and then you don’t have to touch the taps until you’ve washed your hands properly.” Admittedly, this is wasteful, so you could also make sure you disinfect your kitchen taps afterwards.
Kitchen sponges
“I’m surprised new lifeforms don’t evolve in kitchen sponges,” says Chuck Gerba, professor of virology at the University of Arizona. They are prime habitats for microbes.
“They are always wet,” says Markus Egert, professor of microbiology at Hochschule Furtwangen University in Germany. “They have a huge inner surface where a lot of microbes can grow, and you clean a lot of different stuff with them, so the microbes have a lot of nutrients to feed on. And they are rarely cleaned, so that makes them perfect. That’s why there are so many microbes in it within a very short time, billions of microbes. The concentration – not the type of microbes – is similar to a human stool sample.” Studies have shown that sponges can contain harmful bacteria such as salmonella or campylobacter, which can cause severe food poisoning. For elderly people or young children, or those with a weakened immune system, this can be especially dangerous.
If you do use one, you could clean it in the microwave. Wet it thoroughly, put a bit of washing-up liquid on it and microwave it for one minute, and then let it dry out well. “This reduces the number of germs very significantly,” says Egert. But this could eventually prove counterproductive. “The few microbes that survive probably can grow up very fast and so recolonise the sponge. If you do this several times, our hypothesis is that you select for more pathogenic, more resistant microbes than you had before. So you shouldn’t do it too often.” Or preferably don’t use one at all – most sponges are made of plastic and aren’t biodegradable.
Cutting boards
One of the most neglected items in the kitchen, says Gerba, is the cutting board. “People just rinse it off,” he says, “or they’ll cut raw meats and then they’ll make a salad on it, and you have all those cuts and crevices from cutting that make it difficult to clean. Probably the most important thing is putting it in a dishwasher, or rinsing and scrubbing it.”
Toothbrushes
“A toothbrush is going to be mainly oral bacteria,” says Tetro. Some studies have shown a toothbrush can be home to 10m bacteria. “But the microbiome in your mouth will change over time. If you have a lot of sugary, fatty foods, it may help change your microbiome towards bugs that are not so great, and they’ll become even more populous, and then you’re just spreading them in your mouth.”
Give your toothbrush a clean every day. “Run very hot water over the brush and underneath for five seconds. You should also be changing your toothbrush about once a month.” Watch out for your toothbrush holder, too, where gunk accumulates. “All the bacteria in the toothbrush end up growing in the bottom,” says Tetro.
Hairbrushes
Tetro is suspicious of anything named “brush” that is never cleaned. “With a hairbrush, it’s going to be yeast and fungi. After you’ve washed your hair, using a [dirty] hairbrush may transfer it into your hair.” This could lead to dandruff, or scalp infections. It should be enough to clean your hairbrush once a month, says Tetro.
Water bottles
Sometimes dark, always moist, with water left for hours, warming up. Add to that oral bacteria, food particles and (if you’re not a regular handwasher) possibly faecal bacteria, and your water bottle becomes a banquet for germs. If you fill your bottle with protein shakes or sugary drinks, it’s more like an all-you-can-eat for bacteria. One study found 20% of water bottles tested contained coliform bacteria (of faecal origin). Another study found an average water bottle had 20.8m colony-forming units – more than 40,000 times the number on a toilet seat.
“If you drink water from a swimming pool, you should expect to drink poop – but, if it’s your own water bottle, probably not,” says Tetro.
It’s best to pour away old water, wash the bottle in hot water and washing-up liquid and, at least once a week, give it a good scrub with a (clean!) brush. Don’t forget lids, straws and spouts.
Watch straps
Your fancy smartwatch is telling you everything you need to know about your resting heart rate and sleep quality, but it is harbouring a dirty secret – it’s teeming with germs. A 2023 study found that, while staphylococci were expected (they’re naturally found on skin), there were relatively high rates of pseudonomas bacteria (some variants can cause infections in humans) and 60% had enteric bacteria (found in the intestine), including E coli. Rubber and cloth straps were the worst, with gold and silver straps performing well.
Earphones
You handle them multiple times, drop them on the floor, put them in your pocket, share them with other people, and then jam them in your ears – a warm, dark, moist place, home to your usual bacterial flora, and now the venue for a whole host of germs to party to your playlist. One study that swabbed 50 earphones identified fungi and bacteria, including E coli.
Glasses
Again, anything that comes into contact with human skin is expected to be loaded with bacteria, and a study on spectacles found, unsurprisingly, that nose pads and the parts that touched the ears had higher concentrations. While the bacteria detected wouldn’t be a concern to healthy people, the study found about 60% of the bacteria could be risky to people with compromised immune systems. It also identified bacteria linked to eye infections. It found alcohol wipes were the best at decreasing bacterial load, but many opticians say they could damage the lenses and advise warm soapy water and a soft cloth.
Spice jars
A 2023 food-handling study, following people who were making turkey burgers from raw meat, swabbed utensils and kitchen surfaces afterwards and found spice jars were the most frequently contaminated, with nearly half of the objects affected. Your salt and pepper shakers may also be giving you more than seasoning – a 2010 study by ABC News found shakers in restaurants were the second-dirtiest items on the table (after menus), and in a 2008 University of Virginia study, which tested objects that had been touched by cold sufferers, traces of the virus were found on all the shakers.
Reusable shopping bags
“Reusable bags tend to get contaminated with bacteria from raw meat and produce,” says Gerba. “Putting them in a car trunk is like creating an incubator for the bacteria to grow in most climates.” In one of his studies where reusable grocery bags were collected from shoppers and tested, more than half contained coliform bacteria, which probably came from raw meat and other produce, and E coli was detected in 8% of bags. When the team deliberately contaminated bags with meat juices and stored them in the boot of a car for a couple of hours, the bacteria increased tenfold.
“They should be washed on a regular basis,” says Gerba. He favours cotton bags.
Light switches
A team from the University of Houston tested light switches, among other areas including bathroom sinks and floors, in hotel rooms and found they were significant harbourers of faecal bacteria. In another test, nearly a quarter of light switches were found to be contaminated with the cold virus an hour after someone with snotty fingers had touched them.
Remote controls
Your TV remote might be 15 times more disgusting than your toilet seat. A survey for Churchill, the insurance company, found high levels of faecal bacteria on the remotes swabbed. Other surveys have found that between a quarter and third of people never clean their remote, a device that is touched by an average family of four an estimated 21,000 times a year.
Shower curtains
True, it’s not as if you’ll come out of the shower dirtier than you went in, but the curtain may be the dirtiest place in the bathroom. To use our trusty toilet-seat comparison tool, one study found shower curtains had 60 times more bacterial life. That was a laughably small study of three curtains, but it’s obvious they’re a danger zone – people have disgusting shower habits, such as urinating, and bacteria thrive in warm, wet places. So does mould.
“Shower curtains are disgusting,” says Tetro with a laugh. “This is, again, one of those things where, if it’s your shower, your curtain, who cares, right? But a lot of people will share the shower space. As a result, you are going to have a lot more of those human germs.” And not just from people’s hands and faces, he points out. “It’s going to be coming from your whole body, which is why we really should be disinfecting those shower curtains every time we disinfect the tub or the shower stall.” You can also run the shower curtain through the washing machine every so often.
Vacuum cleaners
You should be mindful of how clean any of your cleaning appliances are, from mouldy washing machines to stinky dishwashers. “You should be careful when you empty the vacuum cleaner,” says Gerba. In samples of household vacuum cleaner contents, “we found salmonella in about 10% of them. What you do is you pick up the bacteria and all this nice food for them to eat [in dust and debris], so it becomes a cafeteria for bacteria.” With a bagless cleaner, don’t shake it into your bin in the kitchen – do it outside if you can).
