Hair dyeing
The
future
Recent years have seen an expansion of current technology rather than any groundbreaking new chemistry, at least for commercial applications. The use of pyrazoles as primary intermediates is one example of a modern innovation in established chemistry, while the poor performance (both technically and economically) of indole-based products demonstrates the difficulty of developing successful new chemistry.
Much of this difficulty is due to the uniqueness of hydrogen peroxide,
a cosmetically acceptable reagent which causes the formation of new colours
whilst potentially bleaching an underlying colorant. Patent literature
of the past 10-15 years, however, has several intriguing new technologies,
including the in situ formation of highly coloured Schiff bases. It remains
to be seen which, if any, of these new ideas appear in the marketplace.
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