Everyone has seen those commercials the ones that feature a chirpy spokesperson from your local mattress superstore, telling you that your mattress can double in weight in ten years so you clearly need a new one. But does this really happen?

The idea behind the claim is true. Mattresses gain weight over time as they absorb dead skin , colonies of dust mites (which feed on dead skin ), oil and moisture. But surely if a mattress is gaining weight at a rapid 10 percent per year, someone would have studied the heft? Or mattresses would start breaking bed frames with their bulk? Apparently not.

"To the best of my knowledge, there is no scientific answer to the mattress weight and dust mite query," says Glen Needham, an entomologist at Ohio State University.

"I've heard that mattresses double in weight every 8 years or so, but I'm not aware of any scientific study that backs this up," says Karin Mahoney, a spokesperson with the International Sleep Products Association. She adds that it's well known that beds, in general, are a prime habitat for dust mites where one third of their nasty and brutish life occurs.

According to materials published by Ohio State University, a typical used mattress may have 100,000 to 10 million mites inside. Ten percent of the weight of a two-year-old pillow can be composed of dead mites and their droppings. Mites prefer warm, moist surroundings such as the inside of a mattress when someone is on it. One of their favorite foods is dead skin, and people shed about one fifth of an ounce of the stuff every week, some of which surely ends up flaking into your mattress. (Also gross: About 80 percent of the material seen floating in a sunbeam is, in fact, flakes of dead skin.)

So with all those mites and dead skin, the mattress is bound to be heavier than a new one but doubling in weight is probably ridiculous.

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