88 JOURNAL OF COSMETIC SCIENCE
NOVEL PERMANENT HAIR COLORING SYSTEMS DELIVERING
COLOR WITH REDUCED FIBER DAMAGE
Jennifer Marsh, Ph.D., Chris Gummer, Ph.D. and R. Marc Dahlgren, Ph.D.
The Procter &Gamble Company, Rusham Park Technical Centre,
Whitehall Lane, Surrey, United Kingdom, TW20 9NW
Background:
Use of permanent hair colorants is widespread and allows the consumer to either change their natural hair
color and/or cover gray. However, there are trade•offs that the consumer has to make if she is using these
products on a regular basis. One of the main trade.offs is the fiber damage that is sometimes seen over multiple
uses. This can lead to the consumer experiencing poor hair feel, an increased incidence of split ends and
generally hair that loses some of its healthy appearance and shine. Thus developing hair colorant systems that
allow the consumer to color on a more regular basis yet maintain hair quality is highly desirable.
There are two key chemical processes that take place during the coloring process. The first is the oxidation of
the melanin pigment and previously deposited dyes that lightens the underlying hair color and the second is the
oxidation of the dye precursors to form the coloured chromophores. For both processes the oxidant is essential
and in the majority of retail hair colorants the oxidant used is the combination of hydrogen peroxide with an
ammonia alkalizer at a final pH of 10. Importantly, it is also the oxidant that is mainly responsible for the
damage to the hair fiber which leads to the loss of the hair's strength and healthy appearance.
We have discovered that the uncontrolled production of free radicals during the coloring process can be a
significant contributor to fiber damage. Free radicals are species that are characterised by their high reactivity
with substrates and are well known to be formed by oxidants such as hydrogen peroxide.
There are two key strategies that we have utilised to control the reactivity of the radical species:
(1) Chelation of the redox metal
One important chemistry of hydrogen peroxide is its catalytic reactivity with redox metals such as copper and
iron to form the highly reactive hydroxyl radical (OH*).
H
2 0
2 +Cu +----..Cu2+ +Ho- +HO*
We have demonstrated that the addition of a chelant to the hair colourant such as N,N'•ethylenediamine
disuccinic acid (EDDS) can significantly reduce the formation of the hydroxyl radical by complexing with the
low levels of copper in the hair. We have also shown that the choice of chelant is crucial. In particular, the
chelant must have a high selectivity for complexing to copper, especially in relation to other metals such as
calcium that are commonly found in hair.
The reduction of the formation of the hydroxyl radical has been shown to significantly decrease the fibre damage
from hair colorants when used over multiple cycles. One measure of this damage reduction is via an assessment
of the cuticle quality as measured by the Scanning Electron Microscope (SEM). Chart 1 below shows the benefit
of the EDDS chelant vs a selection of other chelants and the correlation between this benefit and the ability of
the chelant to complex copper in the presence of calcium
Chart I -SEM Grading Data for range of chelants
Chelant (0.05M) added Ratio of Cu to Ca Conditional Binding Constant SEM Damage Index Score*
to retail colorant
EDDS 4
X 1011 6.8
DTPA 4.6
X 107 49.8
EDTA 1.6
X 106 68.6
HEDP 7.7
X 103 61.0
*SEM damage index score based on vtsual assessment of 50 fibers. Fibers were graded on a 4 pomt scale •
low, medium, high damage and stripped. SEM Damage Index ((1 x med)+ (3 x high) +(5 x stripped))/5
NOVEL PERMANENT HAIR COLORING SYSTEMS DELIVERING
COLOR WITH REDUCED FIBER DAMAGE
Jennifer Marsh, Ph.D., Chris Gummer, Ph.D. and R. Marc Dahlgren, Ph.D.
The Procter &Gamble Company, Rusham Park Technical Centre,
Whitehall Lane, Surrey, United Kingdom, TW20 9NW
Background:
Use of permanent hair colorants is widespread and allows the consumer to either change their natural hair
color and/or cover gray. However, there are trade•offs that the consumer has to make if she is using these
products on a regular basis. One of the main trade.offs is the fiber damage that is sometimes seen over multiple
uses. This can lead to the consumer experiencing poor hair feel, an increased incidence of split ends and
generally hair that loses some of its healthy appearance and shine. Thus developing hair colorant systems that
allow the consumer to color on a more regular basis yet maintain hair quality is highly desirable.
There are two key chemical processes that take place during the coloring process. The first is the oxidation of
the melanin pigment and previously deposited dyes that lightens the underlying hair color and the second is the
oxidation of the dye precursors to form the coloured chromophores. For both processes the oxidant is essential
and in the majority of retail hair colorants the oxidant used is the combination of hydrogen peroxide with an
ammonia alkalizer at a final pH of 10. Importantly, it is also the oxidant that is mainly responsible for the
damage to the hair fiber which leads to the loss of the hair's strength and healthy appearance.
We have discovered that the uncontrolled production of free radicals during the coloring process can be a
significant contributor to fiber damage. Free radicals are species that are characterised by their high reactivity
with substrates and are well known to be formed by oxidants such as hydrogen peroxide.
There are two key strategies that we have utilised to control the reactivity of the radical species:
(1) Chelation of the redox metal
One important chemistry of hydrogen peroxide is its catalytic reactivity with redox metals such as copper and
iron to form the highly reactive hydroxyl radical (OH*).
H
2 0
2 +Cu +----..Cu2+ +Ho- +HO*
We have demonstrated that the addition of a chelant to the hair colourant such as N,N'•ethylenediamine
disuccinic acid (EDDS) can significantly reduce the formation of the hydroxyl radical by complexing with the
low levels of copper in the hair. We have also shown that the choice of chelant is crucial. In particular, the
chelant must have a high selectivity for complexing to copper, especially in relation to other metals such as
calcium that are commonly found in hair.
The reduction of the formation of the hydroxyl radical has been shown to significantly decrease the fibre damage
from hair colorants when used over multiple cycles. One measure of this damage reduction is via an assessment
of the cuticle quality as measured by the Scanning Electron Microscope (SEM). Chart 1 below shows the benefit
of the EDDS chelant vs a selection of other chelants and the correlation between this benefit and the ability of
the chelant to complex copper in the presence of calcium
Chart I -SEM Grading Data for range of chelants
Chelant (0.05M) added Ratio of Cu to Ca Conditional Binding Constant SEM Damage Index Score*
to retail colorant
EDDS 4
X 1011 6.8
DTPA 4.6
X 107 49.8
EDTA 1.6
X 106 68.6
HEDP 7.7
X 103 61.0
*SEM damage index score based on vtsual assessment of 50 fibers. Fibers were graded on a 4 pomt scale •
low, medium, high damage and stripped. SEM Damage Index ((1 x med)+ (3 x high) +(5 x stripped))/5
