When you settle in for the night, the last thing you probably think about is what may be lurking in the nooks and crannies of your bedding.
And your ignorance is most likely bliss, because it turns out, beds are ripe - pardon the pun, hotbeds - for microscopic life.
"You have spores of fungi, bacteria, animal dander, pollen, soil, lint, finishing agents of whatever the sheets are made from, colouring material, all sorts of excrements from the body including sweat, sputum, vaginal, and anal excretions, urine milieu, skin cells," Philip Tierno, a microbiologist and pathologist at the New York University School of Medicine, told Tech Insider.
"Plus there are cosmetics that people use - they put oils and creams on their body, all of that is in that milieu."
And there's a lot more, Tierno said, "including food by the way, people eat in the bed. That of course provides a nice environment for these organisms".
Your home's environment is so nice, in fact, that scientists all around the world are trying to identify and quantify the diverse array of pollutants and allergens that not only shack up in your bed, but fawn out across an entire household.
These domestic microbes may negatively (or sometimes even positively) affect our health.
Nasty bacteria from raw meat and vegetables, for example, can live on surfaces for days or even years and cause horrendous cases of food poisoning.
Mould on bathroom surfaces and damp cloths can exacerbate or cause allergies and asthma.
Think this doesn't affect you because you're a relatively clean person? Think again.
Humans naturally produce 26 gallons (98.4 litres) of sweat in bed every year. This moisture, at high humidity, is an "ideal fungal culture medium".
In a 2015 study that assessed the level of fungal contamination in bedding, researchers found that feather and synthetic pillows one and a half to twenty years old can contain between 4 and 17 different species of fungus.
And over time, Tierno said, the amount of fungi, bacteria, and many other debris that accumulate is dramatic.
"You know how Rome was covered and we excavated to find out Rome? That's because gravity [causes debris] to settle over time and bury things," Tierno said.
"The same thing happens with mattresses and pillows: Gravity brings down all this debris and it settles in the core of the pillow and the mattress. And you're inhaling that debris 8 hours a day."
Considering that one in six people have allergies, Tierno says, and the average person spends about a third of their life in bed, scientists are speculating that our beds may be the source of our misery.
"I didn't even mention the dust mites," Tierno said.
"There are dust mite faeces and dust mite debris, which are allergens. Even if you don't have an allergy, you react to it as a normal person."
These allergens may cause you to wake up with a stuffy nose, cause or exacerbate allergies, or aggravate asthma.
Therefore, it's imperative to keep your bed relatively clean, Tierno says, so that you don't overexpose your body to these allergens.
So how often should you wash your bed sheets?
"Stuff like that accumulates to become significant usually between one or two weeks," Tierno said. "Bottom line, they should be washed probably on the average of once a week."
And while there aren't any formal studies on how often you should be cleaning things in your home, Tierno says, this weekly sheet washing suggestion is just a recommendation.
"Certainly if you go one week and two days you're not going to get arrested," Tierno said.
And if you're like most people and have a hard time wrestling with washing your duvet cover, do not fret. You only have to wash that periodically, about every six months, Tierno says, depending on use.
Sweet dreams!
A version of this article was first published in March 2016.
This article was originally published by Business Insider.