Why and how often should you change and wash your bed sheets and pillowcases?

It is a question that can divide people, challenge entire belief systems and potentially tear households apart. Sleep, as you know it, may never be the same again once you start mulling over the query. It is a question so pertinent that we’ve been asked by readers to address it several times.

How often should you change your bed linen, aka bed sheets, pillow and bolster cases, and duvet covers?

Do the experts recommend a certain changing schedule, so we can all sleep better at night knowing that we’ve done our best to weed out dust mites and other microscopic nasties? But first, what’s lurking in those sheets with you in bed?

JUST HOW BAD IS YOUR BED’S GERM SITUATION?

Unless you’re fine sleeping with a legion of germs, you’re looking at some very dirty data. In a study by sleep science coach McKenzie Hyde for Amerisleep, a US mattress and bedding company, bacteria samples were taken from bed sheets over four weeks without washing them, and tabulated in terms of microbial colony forming units (CFU) per square inch. This was what the study found:

PILLOWCASE

BED SHEET

What about the bacteria types that get into bed with you? Basically, bacteria are grouped into four forms: Spherical (cocci); rod (bacilli); spiral (spirilla) and comma (vibrios) or corkscrew (spirochaetes). 

According to Hyde, the most commonly found bacteria sharing your bed were the gram-negative rods (41 per cent), which typically are the culprits behind pneumonia, other kinds of infections and antibiotic resistance. 

And because you tend to keep your face cleaner than the rest of your body, bed sheets were found to be germier. However, that doesn’t mean your pillowcases are yuck-free; they placed first for both rod and spherical types bacteria – which are responsible for skin and throat infections, pneumonia and food poisoning.

WHAT ELSE IS THERE IN BED WITH YOU?

If those numbers aren’t enough to make you nuke your bed sheets, duvet covers and pillowcases pronto, the experts have got more news.

“You shed about 500 million skin cells a day. All these dead cells pile up on your sheets in between washings and dust mites feed on them,” said Malini Thyagesan, a senior lecturer from Republic Polytechnic’s School of Applied Science. “These critters and their droppings can then trigger allergies and asthma, and cause eczema to flare up.”

Your other bodily contributions are just as disgusting. “Sweat and saliva can turn your comfy bed into a petri dish for germs to grow. For instance, lab tests found that swabs from pillowcases unwashed for a week harboured 17,000 times more colonies of bacteria than the samples taken from a toilet seat,” said Malini, referencing Hyde’s article.

After all, sweat is not just water, said Dr Derek Li, a senior family doctor with Raffles Medical, as there are “small amounts of salts and oils in sweat”. That combination, along with the shed dead skin, is where your sheets’ odour comes from, he said.

Dr Li added that if you have sensitive skin, you “may get skin irritation and rashes, or even be more prone to body acne” as prolonged exposure to high concentrations of dead skin cells as well as bodily salts and oils can contribute to clogged pores. 

That’s not all. “With our humid environment, if left unwashed for too long, the sheets can also be breeding grounds for fungi. These can sometimes cause fungal infections on the body,” said Dr Li.

WHAT IF YOU SLEEP IN AIR-CONDITIONING AND DON’T PERSPIRE MUCH?

“Your body has between 2 and 4 million sweat glands that open onto the skin's surface,” said Malini. And these microscopic structures are active around the clock, including at night. Try as you might, the sweat on your body will eventually end up on the sheets and pillows, she said, creating the perfect environment for fungi because moisture, at high humidity, is an "ideal fungal culture medium".

Malini cited a 2006 study that assessed the level of fungal contamination in bedding and noted that feather and synthetic pillows that are 1.5 to 20 years old can contain between four and 17 different species of fungus.

“All pillows had traces of aspergillus fumigatus, aspergillus pullulans, penicillium and other fungi. Some of these micro-organisms are allergenic and may cause breathing difficulties.”

WOULD SHOWERING BEFORE BED HELP?

Theoretically, it would, as showering helps to minimise the amount of dead skin you contribute to the bed sheets, said Dr Li. However, it is difficult to quantify how much help that makes as “we are continually shedding dead skin throughout the day” and night. Malini also agreed that showering helps but will not stop “the number of dead cells shedding when you sleep”.

She is all for a pre-bedtime shower to “rinse toxins, sweat and bacteria off your body before you touch your sheets”. However, don’t go to bed with wet hair as doing so “allows moisture to seep directly into your pillow, creating the perfect environment for unwanted fungi and bacteria”.

If you haven’t had any skin problems with your current frequency of bed linen change, there’s no reason to change it for a theoretical health benefit, said Dr Li.

DOES USING HYPOALLERGENIC PRODUCTS MEAN YOU CAN CHANGE BED LINEN LESS OFTEN?

Malini explained that such products work by creating an environment that allergens find difficult to survive in these ways:

Allergen-resistant materials: They include memory foam, latex or dust-resistant covers to naturally keep away micro-organisms, including pollen, dust, bed bugs and dust mites.

Tightly woven fabrics: Such materials create a barrier against the dust mites that live in your mattress and minimise them from reaching your body. Conversely, they also reduce the amount of dead skin from going onto that dust-mite menu.

Moisture-repelling properties: They don’t retain moisture, which helps eliminate the stuffy, warm environments that dust mites, bedbugs and mould prefer.

But even hypoallergenic bed sheets and pillowcases need regular washing, said Malini. “Hypoallergenic products aren’t 100 per cent allergen resistant and using them alone will not help, unless they are cleaned regularly,” she said. “The frequency of washing depends on how severe your allergies are.”

SO, HOW FREQUENTLY SHOULD WE CHANGE OUR BED LINEN THEN?

No one looks forward to doing chores, which may explain why Singaporeans are keen to find out just how long they can put off the next change of bed linen. 

The frequency is really up to you. “It is highly individualised and there isn’t really a benchmark for this,” said Dr Li. “Certainly, because Singapore is warm and humid, there is a case for changing the sheets more frequently. But it comes down to individual preferences more than objective health considerations.”

In general, the frequency recommendation in Singapore is every one to two weeks, said Malini. “Those who have hypersensitivity should change it every three to four days,” she said. Those numbers aren’t plucked from the air but based on factors such as the aforementioned weather and skin conditions as well as lifestyle, health and bed use.

Eating in bed, leaving your handphone, remote controller, damp towel or clothes on the bed, napping in the day when you’re more prone to perspiring, and letting Fido jump onto the bed are cues that you should change your sheets more often. Ditto if you share your bed with someone who is ill or with a child who is prone to bedwetting, said Malini.

Time to do your chores this weekend!