"It's a zoo inside your pillow, I'm sure," says Ashley Woodcock, a professor of respiratory medicine at the University of Manchester in England who has good reason to know. In a recent study, he and his colleagues broke open 10 bed pillows ranging in age from 18 months to 20 years and analyzed the churning ecosystem inside. Woodcock detected more than a million spores and up to 16 species of fungi, including bread and shower molds, in each cushion. To his surprise, synthetic, "hypoallergenic" pillows consistently harbored more abundant and more diverse fungi than down pillows.
Several ingredients make pillows a rich habitat. Mites eat fungi, and fungi sop up nitrogen-rich dust-mite dung. Both organisms live on shed skin flakes, secretions, and bacteria provided by humans. Add in 20 gallons of sweat soaked up by bedding per person per year, warm the whole brew to a comfortable 98.6 degrees Fahrenheit at 100 percent humidity each night, and, Woodcock says, "it's an ideal culture medium for all sorts of microorganisms."
Woodcock suspects that down pillows may be less hospitable to microbial growth because the tightly woven fabric covers that keep feathers in also keep out spores, mites, dust, and dog and cat dander. The most worrisome and abundant organism Woodcock found in pillows was Aspergillus fumigatus, an asthma-aggravating bacterium that can prove deadly to people with depressed immune systems, such as leukemia and transplant patients. "We're just flagging this," Woodcock says, "so that other respiratory researchers can start taking a real in-depth look."