Dirty hair, probably, carry out the important protective function. The matter is that the secret of sebaceous glands intensively absorbs ozone - the active connection of oxygen capable in high concentration to bring serious harm to health of the person.
Such assumption was put forward by the American scientists from Missouri University. They influenced ozone samples of the dirty and purely washed up human hair.
As it was found out, within 24 hours of experiment, dirty hair absorbed on the average seven times more ozone, than pure.
Ozone is toxic at inhalation: in greater concentration it causes irritation of mucous respiratory ways and damages to lungs. The poisoning with ozone can lead to death.
However, the protective effect of dirty hair, up to the end not clearly has not been studied well: the additional researches lead by scientists, have shown, that in result of interaction with ozone in samples of dirty hair, flying ligaments, which are irritating respiratory ways, are formed.