This caught my eye in New Scientist last week: newscientist.com/channel/he...
Apparently the oils in greasy hair have been shown to absorb around seven times more ozone than clean hair, making the ozone concentration around the head substantially lower. Since ground level ozone has been implicated in triggering asthma symptoms, washing your hair may actually be worsening your asthma!
So come on everyone, throw away your shampoo and cultivate a nice greasy head of hair... it'll have the added bonus that you won't catch colds, either, because no-one will come near you!
Em H