Could you breathe better with dirty hair :

Clean hair has often been associated with proper bodily hygiene. However, a new study out of the University of Missouri suggests that dirty hair may be good for overall bodily health. Why? Dirty hair absorbs seven times more ozone than clean hair does. That means, the ozone levels around the heads of the unwashed are substantially lower than the clean-headed. People with dirty hair would, in theory, breathe in less ozone.

Ground-level ozone is one of the more dangerous pollutants found in big cities. It's so harmful that citizens are often asked not to exercise outdoors during peak-ozone hours. People who live in cities with high levels of ozone are also 25%-35% more likely to die of lung cancer. I don't like those odds.

I would love to tell you that by not washing your hair as often, you will be able to avoid lung cancer. The authors of the study are hesitant to say if there is any benefit to keeping your hair dirty. They did go on record saying that "there may be a net benefit."

Having dirty hair is problematic as well. First off, it's kind of gross. Secondly, 4-oxopentanal, a pollutant, will get caught in your dirty hair and cause respiratory irritation, which is admittedly better than lung cancer but still bad.