439 SUSTAINABLE HAIR
an improved ability for gripping and manipulating the hair. Conventional hair conditioner
products have traditionally been thought of as having an adverse influence on volume
and body where it is felt that deposits potentially weigh down the hair. Here we come to
recognize a second issue where the resulting surface lubrication, while highly beneficial
during detangling, will hinder the ability to grip and manipulate the hair during styling.
To summarize, while visual properties of the hair can be measured and studied their
relationship back to consumer attributes are not straightforward.
HAIR REPAIR AND PROTECTION
By the time that hair emerges onto the scalp, it is biologically inert. It is commonly heard
that “hair consists of dead cells,” which is perhaps an overly dramatic descriptor, but,
unquestionably, there is no more biological activity taking place. The well-being of the
fibers’ structure is then in the hands of the wearer where abstention or minimizing the
highlighted insults will help prolong integrity. The human body has a remarkable ability
to heal itself, but the same is not true for passive hair. Once the cuticle structure has
begun to chip, crack, and uplift, and once the proteins structures of the cortex have begun
to degrade, there is no way back. The one saving grace is that hair continuously grows at
about 0.5 in per month so, the old, damaged hair can be cut off and gradually replaced by
regrowth. Indeed, the hair tips exhibit the highest levels of damage as these are oldest and
have accordingly accumulated the most wear and tear.
“Repair” is a common proposition in the marketing of hair-care products, which
would seem to be opposed to the above discourse. Instead, as already highlighted such
propositions generally relate to the alleviation of symptoms that signify damage. The
lubrication provided by conditioner products can mask all manner of ills. It can smooth
degrading cuticle to mask sensorial negatives and minimize manageability issues. Lesser
grooming forces equate to lower fatiguing forces and an exponentially lesser tendency for
hair breakage and spit ends.
True technical repair of the surface cuticle topography would necessitate feats of
nanoengineering. Chips and cracks would need to be repaired, uplifted scales would need
to be flattened, and lost “tiles” would need to be replaced. The state of the hair surface
is commonly visualized using SEM yet a consequence of this ultra-high magnification
involves only visualizing a minuscule portion of the fiber. Thorough characterization should
involve looking at multiple sites across multiple hair fibers to provide a representative overall
assessment. The highly variable nature of hair means that the occasional highly damaged
spot might be found in hair that generally looks healthy (or vice versa). Unfortunately, all
too often, “evidence” for the above unreal scenarios is presented in terms of SEM images
that have been cherry-picked to tell the desired stories, rather than being representative
renditions.
Similarly, the highly complex, now inert, internal protein structure of hair (see Figure
5) cannot be restored to its initial integrity after “damage” sets in. This structure was
miraculously crafted deep within the hair follicle during growth by processes that we are
just beginning to understand. In recent years, the expression “bond builder” has become
increasingly commonplace in our industry, which, in literal technical terms, implies an
ability to further structure hair proteins to positive ends. Of course, the proposition is
rather nebulous with “which bonds?” rarely being addressed. The creation of any covalent

440 JOURNAL OF COSMETIC SCIENCE
bonds necessitates reactive chemistry, which in turn produces all manner of safety and
regulatory issues. Furthermore, new covalent bonds may not necessarily be advantageous.
Formaldehyde is a chemical that has long been reported to produce new protein crosslinking
in wool and hair40 and has been utilized as a means of permanently straightening hair via
so-called Brazilian Keratin treatments (notwithstanding the serious health implications).
Such treatments can be highly effective, but also result in a dramatic reduction of tensile
properties. It again seems likely that this new term/proposition involves wordsmithing
around the previously discussed relationship between the consumer perception of strength
(i.e., finding broken fibers) and the ability for sizable mitigation via lubricating conditioner
treatments.
In a similar vein, such lubrication can reasonably be expected to help slow certain pathways
of hair’s progressive degradation. Specifically, fibers will be exposed to lesser abrasion and
fatiguing during grooming and other forms of manipulation. This would seem to be a
reasonable and sound foundation for hair protection propositions.
HAIR TYPE
The appearance of hair can vary greatly from one individual to the next. Individual fibers
come in a wide variety of sizes, shapes, and colors and there appears a general presumption
among consumers that such differences must be the consequence of differing makeup. This
leads to the well-entrenched industry concept of “hair type” and the desire to pigeonhole
hair based on any one of a variety of variables (e.g., ethnicity, curl type, color, thickness,
etc.). Yet, historical technical evidence does not support this stance. The overall structure of
all hair abides by the schematic shown in Figure 5, and no general agreement exists among
numerous literature studies that have explored supposed compositional differences in terms
of amino acid levels.5–7 For all its variability, hair would appear to have the same general
makeup no matter how it is classified.
There is strong evidence to suggest that the fundamental shape of hair fibers is dictated by
the manner with which it grows within the follicle.41 Straight hair grows out of straight
follicles and from a symmetrical bulb curly hair grows from curved follicles and an
unsymmetrical bulb. Hair’s natural color is the consequence of melanin pigment granules
located within the cortex higher concentrations produce progressively darker hair, while
low levels produce lighter hair. Despite, the obvious effect on visual properties, the overall
low relative concentrations of melanin, in even the most heavily pigmented hair, leads to
a belief that its presence has no meaningful effect on physical properties. It is not unusual
to find hair fibers with dimensions anywhere between approximately 50 to 100 µm in
diameter yet, they still have the same fundamental structure. Thicker fibers tend to
have a hollow-like center, termed the medulla, which was traditionally thought to have
no meaningful contribution to hair properties. Returning to an earlier point about hair’s
primordial function of keeping the wearer warm, this hollow-like center might be expected
to increase insulating capacity. However, in recent years, we have learned this structure
has a high lipid content,42 which is leading to a rethinking of the passive nature of this
structure. So, while size, shape, and color can make hair look and behave differently, it’s not
because the hair is made of radically different stuff.
It’s worth considering how these seemingly passive properties can sizably impact hair’s
fundamental attributes. Thicker fibers will weigh more, which impacts the way the hair