BOB HIRSHON (host):
Why the sun lightens up hair. I’m Bob Hirshon and this is Science Update.
Michael Wilkes of Ontario, Canada emailed Science Update to ask why hair bleaches in the sun. To find out, we tracked down chemistry professor Ines Joekes at the State University of Campinas in sun-drenched Sao Paolo, Brazil. She’s published several articles on hair photo-bleaching, as it’s technically called, and says there are two processes at work: First, the sun’s UV light breaks down structural proteins in your hair, which creates tiny holes in the hair fibers.
INES JOEKES (State University of Campinas, Brazil):
And these holes act as points in which light is scattered.
That scattering makes your hair look lighter. Additional sun exposure can degrade the melanin pigments in your hair, which changes its actual color. The paler your hair is to begin with, the more noticeable the effect. I’m Bob Hirshon for AAAS, the science society.