How does hydrogen peroxide work to bleach hair?

Bleach is used to lighten hair. wtf

http://chemistry.about.com/cs/howthingswork/a/aa101203a.htm

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Bleach (usually hydrogen peroxide) mixed with ammonia, will open the shaft of the hair. The bleach will oxidize the melanin (there are two types; eumelanin and pheomelanin) and the hair will become a yellowish color (this is because it is the natural color of keratin)

-do some basic research on keratin and the different types of melanin to understand why some people get that reddish/orange colour

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I just want to say, bleach and ammonia mixed together, will kill you.

The fumes are horrible and you will not walk out of the bathroom.

NEVER MIX THEM!