Hair Bleaches or Decoloring Agents
These products provide permanent hair lightening without
the addition of another color.14,15 Bleaching is the most
effective method for lightening hair, whether naturally colored
or dyed.15 The process is the same as the first stage of
dyeing with permanent synthetic dyes.
Hair bleaches contain hydrogen peroxide, ammonia, and
persulfates to enhance their effectiveness and speed up the
process.10,14 Hydrogen peroxide is the oxidizing agent that
releases oxygen from the hair shaft15; hair becomes lighter
according to the amount of oxygen released.10
Bleaching agents oxidize existing melanin.15 During complete
bleaching, melanin granules are completely dissolved,
leaving tiny gaps in the cortex.14
Dark hair requires longer bleaching time15 and goes
through a series of color stages: black to brown to red to
orange to yellow to pale yellow to white.9 This is why, particularly
in very dark hair, partial bleaching may result in
undesirable yellow or orange hues.14
Bleaching reactions are harder to achieve in red hair than
in brown.26 The color obtained is usually flat or dull and
the results are hard to control,35 so bleaching of red hair
is frequently combined with special techniques or coloring
dyes in order to accentuate the hair.14,26