They found that the unwashed hair absorbs about seven times as much ozone as the washed hair.

The Pandrangi/Morrison study (“Ozone interactions with human hair: Ozone uptake rates and product formation”) appears online (February 17, 2008) in the journal Atmospheric Environment.

Pandrangi and Morrison are both members of the Department of Civil, Architectural, and Environmental Engineering at the Missouri University of Science and Technology, Rolla, Missouri.

The two researchers stated, “Ozone is probably reacting with components of hair oil.” [New Scientist, below]

The researchers performed the study because ozone present near the surface of the Earth is known to cause respiratory problems in humans. Studies have previously shown a greater risk of illness and death from the breathing in of large amounts of ozone.

However, the two researchers also stated that after oil from the unwashed hair reacted with the ozone, undesirable products were produced that caused respiratory problems.

They are unsure how much of these undesirable products were produced. Future studies are planned to determine the amount.

Morrison stated, “maybe there's a net benefit, but we really couldn't assume that." He adds, “Clearly our exposure is lower than we think, but our understanding of how it reacts with our body chemistry is pretty limited." [Popular Science “Greasy Hair and Healthy Lungs”]

Morrison suggests that avoiding ozone, especially inside, is wise.

Indoor filtering systems (that do not use ionic filters, which create ozone in their operations) can help to reduce ozone.

Further information is found in the New Scientist article "A fresh excuse not to wash your hair" [March 1-7, 2008, page 20, subscription required, also online at: http://www.newscientist.com/article/mg19726455.200-greasy-hair-makes-for-clean-air.html]