How often you wash your bedsheets depends on a number of factors. The first is whether or not you care about basic hygiene, in which case you will wash them regularly. The second is dependent on how frequently you share your bed with someone else; you might find yourself feeling compelled to wash them even more regularly in between bedfellows, for example. And the third is whether you happen to be a teenage boy, or university undergraduate, which means you might just never wash your sheets at all.

Whichever your bedsheet washing style, it matters much more than you think. And far too many of us are letting ourselves sleep in old, sweaty sheets for longer than we should. According to a survey of 2,000 UK adults conducted by Churchill Home Insurance, people are most likely to wash them every fortnight, with 61 per cent of respondents doing just that. A further 29 per cent said they washed their sheets every week, while a staggering 7 per cent admitted to washing their bedsheets only once every two months or less.

How bad could it be, really, to leave your sheets for a week or two longer than you meant to? What if you don't really sweat much in your sleep? And hey, they still smell clean, right? This is the kind of rationalisation of a dirty person, one who needs a serious wake-up call. Because in actual fact, not washing your sheets regularly can lead to all sorts of issues for your skin, the quality of your sleep, and even your immune system.

"Your skin cells are constantly rejuvenating themselves and this means that when you sleep your body sheds skin," explains Nina Prisk, a skin and aesthetics expert at London cosmetic clinic Update Aesthetics. "These dead skin cells collect in your bedding alongside the sweat, dirt and debris that your body has accumulated during the day. Failure to wash bedsheets regularly can leave skin exposed to dirt, sebum, cosmetic products, and debris which will not only cause dust mites to accumulate, but can result in outbreaks of conditions such as acne, rashes, as well as cause irritation and itching, and flare-ups or eczema."

One thing many of us don't realise is that sleep is an incredibly important time for our skin, generally speaking. "When you sleep your body's natural ability to fight environmental damage and replenish itself is enhanced, meaning it's an optimum time for your skin to refresh and revive," says Prisk. "Sleeping on dirty sheets will negatively impact your body's ability to do this by exposing skin, the largest organ in the body, to bacteria."

That bacteria can have an adverse effect on breathing, too. "House dust mites are a big issue with allergy sufferers, and another reason to regularly wash bedding," says Heather Nixon, sustainability and regulatory manager at eco-cleaning product manufacturer Bio-D. "If you find yourself waking up congested, coughing or having difficulty breathing this could be due to house dust mites."

In addition to all this, sleeping in the same sheets for too long can wreak havoc on your immune system, particularly if you're sharing a bed with a partner who has been unwell. Bacteria and viruses can live on soft fabrics for hours, making it even more important to wash your sheets regularly if you want to avoid getting sick.

Nina Prisk, skin and aesthetics expert at Update Aesthetics

Sleeping in dirty sheets can also impair how well you're actually sleeping. "When experiencing reactions or irritation caused by unhygienic bedding, it's not uncommon for a person's sleep to be impacted due to the discomfort," adds Dr Hana Patel, resident sleep expert at Time4Sleep.

So, how often should you really be washing your sheets to avoid all this? "Washing your bedsheets is a task that should be completed weekly, which can be extended to every two weeks should you not sleep in your bed every evening," says sleep environment expert, Chris Tattersall. How you wash your sheets is important, too. "I would advise checking the label of your bedsheets for guidance, but if they are made of a natural fibre, such as linen or cotton, I recommend washing at 40C on a medium spin cycle, with a non-biological or eco detergent," adds the director of Woolroom. "I would also avoid adding softeners to your wash to avoid using unnecessary harmful chemicals that could irritate your skin."

While many of us reach for softener when washing our sheets, thinking it will make them softer and cosier, using it can actually ruin the sheets themselves, as can the washing process if you don't do it properly, according to Catherine Morris, managing director at Tielle, which supplies bedding at five-star hotels such as The Savoy, The Dorchester and Soho House. "As tempting as it is, fabric softener isn't your linen's best friend as it can coat the threads with a fine residue that ruins its softness and colour," she explains.

"We suggest washing your cotton sheets separately from your other laundry to prevent potential snagging on zips or buttons. Equally, try to ignore the lure of a quick, high-heat tumble dry - we always recommend opting to line dry when possible as it allows the natural air to flow through the threads without the abrasive action of a dryer."

Choosing the right sheets is just as important for sleep quality, which can also maximise hygiene. "The best fabric choices for hygiene tend to be the natural options available, such as cotton or linen," says Jonathan Warren, director and bed specialist at Time4Sleep. "These materials are breathable and moisture-wicking, meaning that moisture such as sweat is less likely to be trapped in the fabric."

It's best to avoid man-made fabrics, such as polyester, which are more challenging to keep clean. "These materials are more likely to trap moisture in the bedding, making them unpleasant to sleep in, particularly in warmer environments when you are more likely to sweat during sleep," adds Warren.

Tattersall agrees that linen is the best. "It is a natural material that has breathable, moisture-absorbent and bacteria-resistant qualities," he explains. "Due to its lignin content, linen slows down the growth and prevents the build-up of bacteria, meaning bed sheets stay fresher and cleaner than other fabric types. Those who suffer from allergies have even reported feeling relieved when using linen in their surroundings."

While the colour of your sheets isn't going to have much of an impact on your sleep hygiene, it can ensure you're getting a good quality sleep. "I would recommend choosing soft, neutral colours for bedsheets," advises Tattersall. "Creating the ideal sleep environment is key to getting a good night's sleep, and part of that is making sure the space you're in is as calming as possible. Soft blues, greens, pinks and neutrals, like beige, grey and white, are all great options that will bring a sense of tranquillity to your nighttime routine, helping to aid better, more restful sleep."

So now that you know, you simply have no excuse. If you're reading this and finding yourself wondering when the last time you washed your sheets even was, step away from the screen and strip the bed immediately.