I love going to sleep. My bed is my sanctuary – and not just mine. When it’s time to turn in, my two cats rush to join me in snuggling under the covers.
Maybe it’s not the most hygienic decision but, I reason, they’re indoor-only cats so they’re not tracking in dirt from outside. Being a non-shedding breed, they don’t even have much by way of fur.
They are, however, still animals. Am I kidding myself?
We all spend a third of our lives in bed – shedding skin, sweating, and depositing all sorts of other matter besides.
Throw in other beings like pets and partners, and account for factors like personal hygiene levels and temporary illnesses, and our beds become microenvironments in and of themselves.
The question of how to keep these environments clean gets far less attention than so-called ‘sleep hygiene’ – the habits and practices that support getting a good night’s rest.
But bed hygiene is just as important for our health, and indeed feeling restored when we wake up.
What counts as good practice, it seems, is a personal matter.
A 2022 YouGov survey of British adults found that more than a third (36 per cent) change their bed sheets once a fortnight, while a little less (28 per cent) do so once a week. A clean two per cent of responders refreshed their sheets more often than that.
But 20 per cent of Britons reported sleeping on the same sheets for three or four weeks, and a not-insignificant four per cent did so for two months or more. Younger adults and men of all ages tended to be most slack.
Meanwhile in the US, a 2017 survey of 1,000 people found that the average American washes their sheets every 24 days.
If they were to see their sheets under a microscope, they might have second thoughts. Our skin is home to millions of different bacteria and fungi (not to mention, when we’re sick, viruses) – some of which make their way onto our bedding each night.
While most skin bacteria are innocuous, potential nasties include intestine-dwellers such as Staphylococcus aureus, causing skin infections; its cousin S. epidermidis (the most frequent cause of infections within hospitals); and some forms of E. coli.
Respiratory viruses such as rhinovirus (behind the common cold) and gut viruses such as norovirus will also make their way to your sheets, says Dr Primrose Freestone, an associate professor in clinical microbiology at the University of Leicester’s department of respiratory sciences.
Our beds, along with our carpets, curtains and other soft materials, are also home to dust mites.
These feed on dead skin cells, bacteria and dandruff, but also breed and deposit droppings. The microscopic fungi that live on our skin also feast on the same matter.
Left unchecked, this cycle of dirtying our bedding (and feeding the tiny beings within it) can exacerbate skin or respiratory conditions and potentially compromise not just our sleep but our health.
So just how unsanitary might our beds be – and what can we do about it?
The dangers of a dirty bed
When I ask Freestone to paint a picture of how dirty my bed might be, I’m not prepared to be haunted by her answer.
“Tube seats and public toilets are cleaned every day. Your bed sheets aren’t,” she says. “I rest my case.”
Yes, those public areas might have higher footfall, but even if we’re not routinely sharing our beds with people or other beings, they still bear the brunt of our own bodily deposits.
Dust mites, feasting happily on our dead skin cells and some bacteria, go on to defecate and multiply. Some people are allergic to these tiny bugs (relatives of ticks and spiders), and experience symptoms common to those of hay fever or asthma as well as disrupted sleep.
If you have acne, eczema or another skin condition, that too may be exacerbated by your bedding, says Dr Chris Callewaert, a senior post-doctoral researcher at the Center for Microbial Ecology and Technology at Ghent University, in Belgium.
While most of the bacteria living on our skin are friendly and even supportive of our health, those linked to acne and eczema will also transfer to bedding and then invade the skin again overnight, he says.
Humidity supports bacterial growth – and beds get sweaty, even in the cooler months. Given we spend so much of the day in bed, Callewaert points out, that’s a lot of sweat. (It’s the reason your sheets can turn yellow, he adds.)
Pathogens, disease and viruses can also be transferred to our sheets, making hygiene especially important when we’re sick or our immune systems are compromised.
A dirty bed may make you more susceptible to these pathogens if you’re vulnerable – for example, as you get older, or if you’re pregnant, have an immune condition, or you’re on chemotherapy.
And, if you’re already sick, there’s also a high chance these bacteria or viruses will be transferred from your bedding to your sleeping partner, Callewaert says.
But there’s a bright side. If you’re in good health, you don’t have much to fear from what lies between the sheets.
“It will not make us sick if we sleep in a dirty bed,” says Callewaert. It may even protect us, he adds, supporting growth of friendly bacteria and training up our immune system to respond to threats.
In this case, the biggest repercussions of sleeping in filth are likely to be social, says Freestone: “You’ll smell.” It might not be dangerous, “but people don’t like it much.”
If your sheets are visibly dirty, smelly or tacky to the touch, it may also negatively affect your sleep.
The short answer: there’s a strong case for keeping your sleeping quarters clean (if the pleasure of drifting off in fresh sheets isn’t incentive enough). It’s a matter of how gross is too gross – and, as per Callewaert’s framework, how clean is too clean.
But you may not know how dirty your bed is in the first place. After all, if we’re only sleeping, where does the bacteria come from?
Read more:
The good side
First, there are dead skin cells. We shed these constantly, accounting for much of the dust in even the cleanest of homes. They radiate off us “like snowflakes” about a metre (3.3ft) in every direction, says Freestone – what’s termed the ‘microbial bubble’.
Then there’s sweat. “Even if it’s cold outside, you’ll still release a couple of hundred millilitres (half a pint) of sweat every night,” says Freestone. This sweat is a food source for the bacteria living on your skin and your sheets, plus it causes body odour.
We also produce sebaceous oils, from glands present everywhere on the body except the hands and feet. What’s more, Freestone adds, people dribble onto their pillows.
No judgement here – but it gets grosser still. “When you fart, you actually expel hundreds of milligrams of faecal matter,” says Freestone. “That might be caught by your underwear, your pyjama bottoms, your nightdress – or the sheet.”
All this might sound disgusting, but the microbial mix of our beds can actually work to protect us.
The skin is the largest organ and home to approximately 10 trillion bacteria, the overwhelming majority of which support its functioning and even our all-round health.
“The whole immune system that’s present in the gut is also present more or less as a copy-paste of the same in the skin,” says Callewaert. The gut microbiome affects our skin, and vice versa.
As we shed dead skin cells and other matter besides, “our bed sheets become more like us,” he says, supporting the production of good bacteria.
By the same token, if we’re too zealous about sterilising our bedding, it might encourage new and potentially hostile bacteria to take their place.
Healthy adults are more than capable of fighting off minor threats from a somewhat dirty bed. They can even be beneficial, Callewaert says, “because then our immune system is tested and trained.”
Bed buddies
People who live together end up sharing some of their microbial matter, and two in a bed means double the deposits. Sexual fluids are conducive to fungal and bacterial growth, too.
Heterosexual couples, in particular, may want to clean their sheets more regularly because of the differences between men and women’s microbiomes. “Your hormonal status influences what grows on you and within you,” explains Freestone.
Even same-sex partners will have predominantly different skin microbiomes because of factors like washing frequency and different diets. “One person’s bacteria can be another’s pathogen – that’s why we don’t share toothbrushes,” she adds.
As for parents who let their children into their beds, kids’ still-developing immune systems (and their concept of personal hygiene) mean they can be susceptible to infection and spreading it around their households. Yield at your own risk.
I’m starting to feel grateful for my cats – but Freestone says they can’t be discounted, even if they aren’t tracking in matter from outdoors (and are follicly challenged). “They’re different species from us, so they’ve got different bacteria.”
More to the point: there are unsavoury behaviours animals routinely indulge in that humans typically don’t. “Pets lick their bottoms, then they lick you, or their fur, then they lay on your sheets,” Freestone says.
Even setting aside faecal matter, dog and cat saliva contains about 600–700 different species of bacteria, fungi and other microorganisms, as well as pathogens that can cause disease in humans.
But, again, we end up sharing microbes with the animals in our household, just as we do with people, creating “a mix of bacteria” that Callewaert believes is more likely to be beneficial than not.
A hitchhiker's guide
For those without pets, the big battleground of good bed behaviour is whether it’s ever okay to eat there. Freestone admits she occasionally indulges in chocolate in bed.
But any leftovers will be snapped up by bacteria and fungi as a palate cleanser from their standard diet of your skin and sweat. “You’re just promoting the growth of anything that’s already there,” she says.
Then there’s the question of whether the clothes you wear outside, bags and – heaven forbid – shoes are ever permissible on your bed.
If there’s a risk of pathogens being transferred from the outside environment – for example, there’s been a bug going around the office, or you work or commute in less-than-hygienic conditions – then yes, Callewaert says, caution might be advised.
But in general, he’s relaxed: “The bacteria that are sitting here on my chair are not really different from the bacteria that are on my bed.”
Freestone maintains more of an inside-outside boundary, but says dirt is less of a concern than tiny hitchhikers. “There are bed bugs on buses, on trains, on the London Underground – if there are people, there will be bed bugs.”
Contrary to popular view, these aren’t a sign of unsanitary conditions – but once they’ve bedded in (so to speak), they can be fiendishly hard to eradicate.
Most infestations of private homes begin with a pregnant female bed bug stowing away inside luggage or on clothes.
To stop them coming home with her from holidays (travellers often encounter bed bugs in hotel rooms), Freestone wraps her suitcase in clingfilm and stores it off the floor.
And if there are telltale specks on the mattress, “I’ll leave as soon as possible,” she says.
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- Bed bugs UK guide: How to get rid of them, and how to spot an infestation
- Why don't we fall out of bed more often?
Clean routine
Of course, personal hygiene plays a part in how dirty our beds get, but when it comes to the optimum night-time routine, there’s no clear-cut case for whether to shower at night or in the morning.
Freestone opts for the latter, because of the sweat we produce overnight. “Showering at night is a bit pointless because in the morning you’re going to smell anyway.”
Callewaert personally showers at night. “You have less bacteria that will go into the bed sheets.” It comes down to personal preference – at least from a bed hygiene perspective.
Pyjamas will retain some of the shed skin cells, sweat and other debris you produce overnight – while also letting a lot through to the sheets. Relative to tiny bacteria and fungi, the holes within woven materials are the size of a TV screen, says Freestone.
Even so, it’s more hygienic to wear pyjamas than not. “You reduce the amount of faecal material you would deposit on the sheets,” she says.
And yes, you probably want to wash your lovely silk PJs regularly, too – Freestone says every few days at the most.
“It’s like your underwear: how often do you change them? The answer should be every single day, because of what you deposit on them.”
Airing dirty laundry
Flinging open a window will obviously help with any smells, but airflow is also important for creating a better sleeping environment, and not just because cooler rooms are associated with better shuteye.
Along with the complex mix of bacteria, fungi and allergens, our bedding and mattresses also contain chemicals such as flame retardants that break down over time, says Dr Matthew J Reid, an assistant professor in psychiatry at the Johns Hopkins University School of Medicine in Baltimore, US, and an executive committee member for the British Sleep Society.
Our exposure to these pollutants is amplified by the heat generated by our sleeping bodies, creating what’s known as a ‘buoyant thermal plume’ emanating from around our heads.
“You get this heat column, kind of like smoke coming out of a chimney,” Reid says – and, every night, we breathe it all in.
Not washing your bedding creates “a build-up of all of those materials, which is just going to increase the density of them in that thermal plume and breathing zone”, he says.
This has the potential to negatively affect how well we breathe during sleep, increase the risk or frequency of sleep apnoea events, and trigger existing allergies or sensitivities.
“Regulating that external environment you’re breathing in is really important,” Reid says.
Air circulation also helps manage sweat and other moisture inevitably soaked up by our beds – one reason we elevate mattresses off the ground, Callewaert says.
“It’s important to make sure that humidity is not caught in there, otherwise we have bacterial growth.”
Both Callewaert and Freestone suggest exposing your sheets to help them, and your mattress, dry out after you’ve slept.
In other words, wait at least 30 minutes before making up your bed each morning. (Callewaert notes this isn’t necessary if your home is particularly well ventilated).
Pillows become particular hothouses, as they soak up oils from our face and scalp, tears, drool, and any skincare or hair products we wear to bed.
“Fungi can end up growing in the interiors,” says Freestone. She washes her pillow (and sofa cushion) inners at least once a month, and the cases more frequently.
Sheet schedule
So, finally, the question on everyone’s minds: how often do you need to wash your bedding?
By this point I’m practically itching to change my sheets, and I bet you are too. I’m among the majority of Britons who do so fortnightly – but Freestone suggests once a week might be a better rule of thumb.
Some sources recommend changing the sheets as often as every three to four days, though that might be overkill if you’re healthy with good personal hygiene.
“It depends on the wear and the footfall,” says Freestone. “If the weather is very hot, you sweat a lot, or you’ve got asthma or any kind of health problem, you’re certainly advised to change your sheets every two to three days, and sometimes even every single day.”
It’s the same for pillowcases, but you can be more relaxed about duvet covers and inners, quilts, blankets and other bedding that gets less wear and tear, she says.
Washing your sheets more often won’t necessarily mean you have to replace them sooner – it may even extend their life as some bacteria and fungi produce enzymes that break down cotton.
Hotter washes of 55°C (131°F) or above will eradicate more bacteria, but Callewaert says that’s not strictly necessary. Indeed, we want to avoid creating a too sterile environment, lest we change our microbiome for the worse. “Bacteria are good for us, and for our skin as well.”
Washing at 30–40°C (86–104°F) with an enzyme-based laundry detergent is generally adequate unless you’re sick or there are other health concerns at play. “If there’s no need to sterilise, we don’t have to do it,” says Callewaert.
More important is being prompt to remove just-washed bedding from the machine and dry it properly to decrease bacterial load and odour, he says.
Freestone is more in favour of washing on hot as standard and suggests adding a laundry sanitiser to colder washes for an extra layer of protection.
One thing both experts agree on is that the bliss of sliding in between clean sheets, which seems to support a good night’s sleep, is mostly psychological.
If you’re happy with the frequency of your bedding changes, sleeping soundly and experiencing no ill effects to your health or otherwise, then keep doing what you’re doing, Freestone says.
“But when your sheets have got filthy, that’s potentially when you need to start worrying about what it’s going to do to your health. Remember, you’re breathing this in all the time.”
After all, going to bed should be a restful, restorative experience – even a pleasure. Sweaty sheets tend not to be conducive to sweet dreams.
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