You’ve probably heard before that dust is mostly made of dead skin cells. It’s just one of those factoids that sticks around because it’s both intuitive and gross. But according to many sources on the internet, that’s just a myth. Science educator Derek Muller, however, says that is indeed—to some extent—the case. And he shows the calculations for his conclusion in his latest video to prove it.
Muller recently posted the answer to the question “Is dust mostly skin?” to his YouTube channel, Veritasium. For those unfamiliar, Muller is a PhD in physics responsible for countless other videos explaining the incredible physics of our world. Previously, Muller has covered everything from self-driving cars to the beauty of turbulence.
Muller begins his deep dive into dust by defining the standard for dust-particle sizes. The educator notes that the International Organization for Standardization says dust consists of particles 75 micrometers or less in diameter—or roughly the width of a human hair. Other sources, however, say dust particles can be up to 2,000 micrometers or less in diameter.
Despite the discrepancy in standardization, the key property of dust, Muller says, is its settling velocity. Settling velocity determines how long a particle can stay in the air. Dust varies in shape, size, and density so much; this is the most efficient way to delineate what makes up the fine filth and what doesn’t.
Subsequently, dead human-skin cells, by any of these measurements, count as dust. And since an individual with the average amount of skin surface area sheds 1,000 skin cells per hour, that means a lot of the dust in your home, and many other places, truly contains a lot of dead skin.
“[T]he debunkers are debunked,” Muller says in the video, adding that “dead skin cells do make up a significant portion of household dust.”
Perhaps the grossest calculation Muller makes gives insight into just how much all of this sloughed-off dead skin weighs. If two people slept on a mattress for a decade, and shed all of their skin into it, it would gain seven pounds. Just from dead skin. Incidentally, you may have trouble sleeping tonight.
What do you think about this scientific investigation into the amount of skin cells in dust? Are you shocked to learn that this “myth” is, essentially, true? Shed some opinions in the comments if you can stop scratching yourself!
Feature image: Veritasium