“After 8 years, an old mattress becomes a heavy weight, from pounds of dead skin, gallons of sweat, and millions of dust mites that accumulate inside it!” So claims an ad for the concerned Mattress Firm—your salvation is, of course, to purchase a fresh, unsoiled mattress from them. But is this true? Do our mattresses really suck up pounds and pounds of ick over the years?
Probably not pounds per se, but they do become … occupied. Even if you curl up to sleep solo, you’re not alone. Besides collecting the skin flakes, sweat, and oil you secrete while counting sheep, your mattress is also home to hundreds of tiny creatures called dust mites. The mites are very small (less than a millimeter long) and difficult to see with the naked eye. Their diminutive size means they can penetrate through most sheets to live out their entire life cycles in your bed.
“Every mattress is a crime scene in terms of how it gets inoculated with mites,” explained Glen Needham, a retired professor of entomology at Ohio State University. Dust mites might find their way to your bed by clinging to your clothes or even your beloved pet. “All you have to do is get a female dust mite to start laying eggs, and pretty soon you have a starter set going in your mattress,” Needham said.
Mites feed on the dead skin cells that we shed naturally in our sleep. Their mouths are designed like chopsticks in that they don’t open very far, so thin, protein-packed flakes of skin—Needham compared them to Pringles—are their ideal meal. Your body also emanates the humidity dust mites need to survive: Instead of drinking water, they have an apparatus that sucks moisture straight from the air, Needham explained. In other words, your mattress is a dust mite’s ideal habitat; when you go to sleep, you provide all the food, water, and warmth a mite could ever want.
A spokeswoman for Casper mattresses, a company so confident in its mattress design that it only makes one, speculated that spring mattresses are more susceptible to mite infestations because they have “more air pockets where dust and skin cells can accumulate over time.” But Needham postulated that foam mattresses might be even more attractive to mites, and a study on dust mites published in 2002 confirmed his suspicions.
“Most foam cells are closed cells, so mites can’t go down into the foam very far; but because of that they probably hold heat better,” he said. “They still trap skin scales, and they’re warmer, so I speculate that mite populations would do better on a foam mattress.” Needham, who’s only experimented on traditional mattresses, added that mites prefer the polyester layer just below the mattress ticking. (Note to those with pillow-top mattresses: The more pillow-y your mattress the more polyester it contains, therefore the higher your mite population.)
The good news is that, unless you’re allergic to them, dust mites cause relatively little harm. They don’t bite and they’re not parasitic—the worst thing that can come from a dust mite infestation, comforted Needham, is an unpleasant odor. Those who are allergic (about one-third of individuals tested) don’t always have symptoms. However, the proteins in dust mite feces can cause allergic reactions like watery eyes, a runny nose, and, in severe cases, asthma attacks.
Mattress companies like to use dust mites as scapegoats to peddle their products: A common statistic cited by people like Larry over at Sit ’n Sleep is that your mattress doubles in weight every eight years thanks to a combination of human debris and dust mites. Although dust mites do shed their skin, defecate, and reproduce within your mattress, Needham reckoned a significant increase in weight due to mites is unlikely. “The mattress industry has used that statistic to creep people out,” he said. “I don’t think anyone has ever done a real calculation. It’s an eye-catcher, and they’ve probably made estimates based on how many skin scales a person discards and how that debris is converted.”
Read more from The Drift, Slate’s pop-up blog about sleep.
So next time you’re feeling lonely at night, cuddle a little closer to the tiny, eight-legged bugs waiting just centimeters away from you. “You don’t think of a mattress as having an ecosystem,” marveled Needham, “but it really does.”