We shed skin constantly -- each of us replacing our outer layer of skin every two to four weeks -- and all of those skin flakes may help reduce levels of certain pollutants in indoor environments.
Substances in human skin oil are significant components of indoor dust, a new study found. And those substances are known to remove ozone from the atmosphere. Just by sitting there, in other words, you help cancel out some of the ozone in the room.
But floating flakes of skin might also do harm. Byproducts form as skin substances interact with ozone. Scientists don't yet know what the effects of those reactions might be.
"These results are a reminder that humans leave their skin flakes in the rooms they occupy," said lead researcher Charles Weschler, a chemist at the University of Medicine and Dentistry of New Jersey.
"What one person sheds may be an allergy trigger or source of harmful microbes for another occupant," he added. "Keeping our indoor environments clean remains as important in 2011 as our grandparents told us two generations ago."
Ozone is a major component of smog, and exposure to it has been linked with a greater risk of lung irritation, asthma, heart attacks and death. Removing ozone from the environment, on the other hand, can reduce those risks and scientists have long wondered how human skin might help.
Ozone is quick to react with a few ingredients in human skin oils, including certain fatty acids and especially a substance called squalene. Previous research has shown that the simple presence of humans can reduce ozone levels in indoor situations.
A simulation study, for example, found a plume in a region around the body where ozone levels were lower compared to other areas because of reactions with skin oil, said Glenn Morrison, an environmental engineer at the Missouri University of Science & Technology in Rolla, who led that work.
In another study published several years ago, Weschler and colleagues used simulated airplane cabins to show that the skin of passengers works like a sponge to remove a large portion of the ozone from aircraft environments. But the study also found that these chemical reactions produce byproducts with unknown and possibly harmful effects on health.
For the new study, Weschler's group looked at data collected as part of an ongoing project in Denmark that is investigating potential links between indoor environments and children's health problems, especially allergies and asthma. In particular, they focused on dust samples collected from the bedrooms of 500 kids, ages three to five, and from 151 daycare centers that those children attended.
Almost every sample contained large proportions of squalene and cholesterol, the researchers reported in Environmental Science & Technology, suggesting that human skin flakes make up much of the dust that settles on indoor surfaces.
And while skin cells contain more squalene than cholesterol, the researchers found the opposite ratio in dust. That might be because cooking and other activities also release cholesterol into the environment. It could also be because ozone in the buildings is sucking up squalene. This was the first study to look at skin-derived substances in indoor dust.
The next question, Morrison said, is whether chemical reactions between skin and ozone make air quality better or worse inside buildings. Removing ozone should be a good thing. But byproducts produced by ozone-skin reactions are known to be strong lung irritants.
For now, along with previous work, the new findings are "really revealing how the human body is a big part of influencing our environment," Morrison said. "This is a pretty important outcome if you are trying to understand ozone exposure and other things, because we're part of the equation and we've basically been ignored."