Hair coloring
has been practiced for thousands of years, with the most famous early
practice being the use of henna preparations by the early Egyptians.
This natural dye imparted redorange high-lights to hair, and still today
henna (Lawsonia inermis), henna extract and the actual active color
ingredient of henna, (2-hydroxy-1,4-naphthoquin-one), are
recognised cosmetic ingredients. However, natural colorants make up only
a miniscule part of the hair color market, due to the far superior
performance and versatility of synthetic colorants. The development of
modern hair colorants began in the late 19th century when synthetic
organic compounds were first used for this application. Modern products
allow the user to achieve everything from temporary color addition
through to more durable color highlights and grey coverage to lasting
color changes. Estimates for the usage of hair color throughout
industrialised countries range upward to 50%.
Uniqueness of hair dyeing
The dyeing of 'living' hair fibres offers a singular challenge to the
colorist, and several factors set this technology quite apart from other
dyeing procedures. The option, indeed the necessity, of periodic
reapplication is notable. This is less to restore faded color than to
apply color for the first time to new growth hair. This constant
development of new substrate is perhaps the most peculiar feature of
this dyeing category. Repeated application does, however, allow the
industry to use dyes with lower fastness than in other categories. Hair
fibres as a dyeing substrate are rather complex. The fibres themselves
are heterogeneous cross-sectionally and even, to some extent, from root
to tip (see Figure 1). The outer layer, or cuticle, consists of
overlapping cells, generally five to seven layers, while the inner
cortex has longitudinally arranged keratinous fibrils within elongated
corticular cells. It is the cortex which contains the natural melanin
colorant. New growth hair near the root has a tight corticular structure
while the weathered and treated tip ends are far more porous, thus
making uniform dyeing quite challenging under the mild conditions of
product use. Additionally, hair may vary substantially in both chemical
and physical composition, depending on race, hair color, environment and
a variety of other factors. Conditions of application are quite
restrictive allowing very limited ranges of pH and temperature and, to a
lesser extent, time. Only physiologically accept-able environments are
used, and limited adsorption and/or diffusion at ambient temperature
precludes the use of many traditional dyestuffs. Dyebath exhaustion is
practically non-existent. The process may be more accurately described
as staining, since significant amounts of dyestuffs are washed away and
not utilized. Finally, the exposure of the user to both dye precursors
and finished dye-stuffs demands rigorous toxicological testing and
acceptable profiles for all materials.
Types of hair colorants
There are three general categories of hair colorants, defined by the
duration the color remains on the hair. However, the distinctions
between these various categories have been somewhat blurred in the past
1015 years, due to new dyestuffs and improved formulations.
Temporary coloring
Temporary colorants are removed by the first shampooing. These products
are usually called 'color rinses' and use high molecular weight ionic
colorants which are deposited on the surface of the hair with no
penetration into the cortex. These are acid dyes with minimal affinity
for the overall anionic nature of hair, and are generally used for a
specific event or occasion. A second class of temporary colorants are
large cationic basic dyes with at least an ionic
attraction for hair, thus somewhat better fastness, but still only
surface deposition. Products formulated solely with D&C† and/or
FD&C†dyes do not require a preliminary patch test, usually performed 48
h prior to application, to check for allergic response. This test is
required for other hair colorant products, and not having to perform it
makes these products simpler and more appealing to use. Their limited
efficacy, however, means that users often move onto a different, longer
lasting hair colorant type.
These
are colorants certified by the US Food and Drug Administration (FDA) for
use in drugs and cosmetics (D&C) or foods, drugs and cosmetics (FD&C).
Each potential FDA-approved colorant is tested for minimum assay and
maximum impurity levels, which vary for each compound, and are certified
to meet these standards.
ITC Profile
Contacts
Send Enquiry
ITC Home Page
|
|