Solar ultraviolet protection provided by human head hair.

The solar erythemal UV irradiances through human hair and the protection from UV provided by human head hair have been investigated for a solar zenith angle (SZA) range of 17-51 degrees for the conditions of a head upright in full sun, a head upright in shade and a head in full sun tilted toward the sun. The two hair lengths investigated were 49.1 +/- 7.1 mm for the short type and 109.5 +/- 5.5 mm for the long type. For the head upright in full sun, the irradiances through the hair ranged from 0.75 to 1.4 SED h(-1) for SZA <25 degrees and <0.6 SED h(-1) in shade. The ultraviolet protection factor (UPF) ranged from approximately 5 to 17 in full sun, with the UPF increasing with higher SZA. The longer hair provided a lower UPF than the shorter hair and for the head oriented toward the sun, there was a marginally lower UPF than for the upright head. This research shows that the UV exposure limits to the scalp through hair can be exceeded within short timeframes and provides important information to assist employers to comply with Workplace Health and Safety legislation.