Healthy Hair: What Is it?

Abstract

Shiny hair with a smooth texture and clean-cut ends or tapered tips is generally perceived to be healthy. Hair texture and shine relate to hair surface properties, whereas the integrity of hair ends relates to the hair cortex. Hair can be straight, wavy or curly, blonde, black, brown, red, gray white, and its natural variations are important to our identity. Manipulation of the normal structure of the hair shaft is epidemic and dictated by culture, fashion, and above all, celebrity. Although cosmetic procedures are intrinsically safe, there is potential for damage to the hair. Loss of lustre, frizz, split ends, and other hair problems are particularly prevalent among people who repeatedly alter the natural style of their hair or among people with hair that is intrinsically weak. This may be due to individual or racial variation or less commonly an inherited structural abnormality in hair fiber formation. Hair health is also affected by common afflictions of the scalp as well as age-related phenomena such as graying and androgenetic alopecia. Hair products that improve the structural integrity of hair fibers and increase tensile strength are available, as are products that increase hair volume, reduce frizz, improve hair manageability, and stimulate new hair growth.

Full text

Healthy Hair: What Is it?
Rodney D. Sinclair
1
Shiny hair with a smooth texture and clean-cut ends or tapered tips is generally perceived to be healthy. Hair
texture and shine relate to hair surface properties, whereas the integrity of hair ends relates to the hair cortex.
Hair can be straight, wavy or curly, blonde, black, brown, red, gray white, and its natural variations are important
to our identity. Manipulation of the normal structure of the hair shaft is epidemic and dictated by culture,
fashion, and above all, celebrity. Although cosmetic procedures are intrinsically safe, there is potential for
damage to the hair. Loss of lustre, frizz, split ends, and other hair problems are particularly prevalent among
people who repeatedly alter the natural style of their hair or among people with hair that is intrinsically weak.
This may be due to individual or racial variation or less commonly an inherited structural abnormality in hair
fiber formation. Hair health is also affected by common afflictions of the scalp as well as age-related phenomena
such as graying and androgenetic alopecia. Hair products that improve the structural integrity of hair fibers and
increase tensile strength are available, as are products that increase hair volume, reduce frizz, improve hair
manageability, and stimulate new hair growth.
Journal of Investigative Dermatology Symposium Proceedings (2007) 12, 2–5. doi:10.1038/sj.jidsymp.5650046
INTRODUCTION
This review aims to help the clinician to understand the
complex interplay between the various medical and bio-
logical factors, scalp care habits, hair care procedures and
environmental factors to hair health.
Hair is an important component of body image. It is one of
few physical characteristics we can change and manipulate
to the dictates of culture and fashion. Hair cosmetics are
widely used to alter the physical and mechanical properties
of hair, which are dependent on internal structural organiza-
tion and protein constituents.
HAIR STRUCTURE
Hair consists of an outer hydrophobic lipid epicuticle, a layer
of flattened overlapping cuticle cells surrounding the
elongated polyhedral cortical cells. The normal cuticle has
a smooth appearance, allowing light reflection and limiting
friction between the hair shafts It is responsible for the lustre
and texture of the hair. (Draelos, 1991) The cuticle may be
damaged by frictional forces like brushing. The cortical cells
surround an optional and often discontinuous central
medulla. The cortical layer determines many of the mechani-
cal properties of the hair. The surface of the hair is covered in
a covalently bound, monomolecular layer of a unique,
branched, fatty acid – 18-methyl eicosanoic acid (Figure 1).
The cortex consists of closely packed spindle-shaped
cortical cells filled with keratin filaments that are orientated
parallel to the longitudinal axis of the hair shaft (Dawber and
Messenger, 1997), and an amorphous matrix of high sulfur
proteins (Dawber, 1996). The intermediate filament hair
keratins (40–60 kDa), comprising 400–500 amino-acid resi-
dues in heptad sequence repeats, form hard keratin polypep-
tide chains which pair together to form protofilaments
(Dawber and Messenger, 1997). The keratin chains have a
large number of sulfur-containing cysteine residues. Cysteine
residues in adjacent keratin filaments form covalent disulfide
bonds forming a strong crosslink between adjacent keratin
chains. (Feughelman, 1977) The disulfide bonds contribute
much to the shape, stability, and texture of the hair. These
disulfide bonds remain intact when the hair is wet allowing
the hair to resume its original shape. Other weaker bonds link
the keratin polypeptide chains together such as Van der Waal
interactions, hydrogen bonds, and Coulombic interactions
known as salt links. (Feughelman, 1977) These weaker bonds
can be overcome with water.
Combinining the outer, intensely hydrophobic layer and
the cortex confer the physical properties of lustre (shine) and
volume (body) so essential for the appearance of ‘‘health’’
(Figure 2).
HAIR PHYSICAL PROPERTIES
When wet, hair can be stretched by 30% of their original
length without damage; however, irreversible changes occur
when hair is stretched between 30 and 70%. Stretching to
80% causes fracture (Dawber and Messenger, 1997).
Hair is porous: damaged hair is intensely so. Water
absorption causes hair shaft swelling. And when soaked in
water hair weight increases by 12–18%. Wetting and
subsequent drying in a predetermined position are basic to
hair styling. Wet hair has higher combing friction than dry
2 Journal of Investigative Dermatology Symposium Proceedings (2007), Volume 12 & 2007 The Society for Investigative Dermatology
1
Department of Dermatology St Vincent’s Hospital, The Skin and Cancer Foundation of Victoria and The University of Melbourne, Victoria, Australia
Correspondence: Professor Rodney D. Sinclair, Department of Dermatology, St Vincent’s Hospital, Victoria, 3065, Australia.
E-mail: sinclair@svhm.org.au

hair. Combing wet hair is more likely to stretch brittle hair to
its breaking point (Draelos, 2005).
Hair shafts, when dry produce static electricity. Static can
cause hair shafts to repel, creating flyaway hair. Moisture
reduces static and frizz (Draelos, 2005).
Hair shape, especially in cross-section influences wave
and curl, light reflection and therefore hair shine, sebum
retention, and ease of grooming (Draelos, 2005).
COSMETIC ALTERATION
Successful cosmetic alteration requires chemical processes that
alter the normal structure of the hair shaft (Harrison and Sinclair,
2004). For a permanent change in the hair, the chemical
reaction of coloring, perming, or straightening must occur in the
cortex. Bleaching, perming, and straightening alter the physical
properties of hair. The f-layer is removed with any chemical
procedure and the internal disulfide bonds of the cortex are
broken in hair styling with permanent waves. Excessive or
repeated chemical treatment, poor grooming habits, and
environmental exposure produce changes in hair texture and
if extreme can result in hair breakage. These changes can be
seen microscopically as ‘‘weathering’’ of the hair shaft and
contribute to rendering the hair structurally weaker, more prone
to tangling, and rougher in appearance (Figure 3).
Different types of hair have varying affinity for the different
coloring and waving methods. Damaged hair also has a
different affinity for hair products (Brown, 1977).
In addition hair strength and resistance to damage by
exogenous factors show racial as well as individual variation.
Inherited structural abnormality in hair fiber formation are
rare and beyond the scope of this article.
In people of African descent, permanent hair loss in the
form of hot comb alopecia and possibly also central
centrifugal alopecia are recognized, rare consequences of
hair straightening procedures (Sinclair et al., 1999). Traction
alopecia is potentially reversible hair loss that occurs as a
consequence of certain hair styles (Sinclair et al., 1999).
WEATHERING
Weathering is the progressive degeneration from the root to
the tip of the hair of the cuticle and then later the cortex due
to routine everyday wear and tear.
Although all hair exhibits some degree of weathering,
longer hair, subjected to repeated insults, inevitably shows
more severe changes of weathering (Figure 2) (Gummer,
1999). Features of weathering include damaged cuticles,
longitudinal fissures known as spilt ends and transverse
fissures resembling the nodes seen in trichorrhexis nodosa
(Dawber, 1996).
The hair shaft documents the history of the cosmetic
practices of an individual (Gummer, 1999). Hair grows at
E 1 cm per month, and so the tip of a hair 24 cm in length, is
in fact 2 years old (Gummer, 1999). Therefore, newly growing
roots have different properties to the hair tips. The older part of
the hair shaft, particularly the tip has undergone over 700
Figure 1. The f-layer – 18-methyl eicosanoic acid is intimately bound to the
exo-cuticle and intensely hydrophobic.
Figure 2. Healthy hair as evinced by shine and body.
Figure 3. A significant degree of weathering to the hair shaft. Most
weathering is self-inflicted.
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RD Sinclair
Healthy Hair

washes, the application of hot styling implements and other
cosmetic procedures such as bleaching, permanent coloring
and perming, and may show features of weathering, whereas
the root may be less porous and have different chemical
properties (Gummer, 1999).
SPECIFIC CAUSES OF WEATHERING
Bleaching
Bleaching oxidizes the existing melanin in the cortex. Darker
hair requires longer bleaching times. Red hair is more difficult
to bleach than brown hair. The oxidization reaction destroys
some of the disulfide bonds within the keratin and can
damage the cuticle making it more porous (Bolduc and
Shapiro, 2001).
Permanent styling
Permanent styling is achieved through the use of permanent
waving or straighteners. Both processes involve denaturation
of the structural disulfide bonds and as such have the
potential to cause significant damage to the hair (Zviak, 1986).
They also remove covalently bound surface lipids, changing)
the surface of the hair from hydrophobic to hydrophilic
to allow the interaction of water and styling products
(Gummer, 1999).
Permanent waving or perming changes the shape of the
hair so that the new shape persists through several shampoos.
Structural disulfide bonds need to be broken (Borish, 1977;
Gray, 1997). The neutralization process may be more
damaging than the thiol reduction and free radicals may
cause some of this damage (Borish, 1977). Newly grow-
ing hair will not be affected and so the perm eventually
grows out.
Chemical hair relaxing or lanthionization is similar to
permanent waving, but the hair is permanently straightened
instead of curled.
Hair straightening needs to be repeated every 4–6 weeks
and only new regrowth needs to be straightened, otherwise
damage to the hair can occur (Ahn and Lee, 2002).
Individual and racial variation. Mongoloid hair is straight
and is more commonly dark brown in color than black. It has
a circular cross-section. Caucasoid hair has an elliptical
cross-section and may be straight, wavy, or curly. The color
may vary from red, blond, brown to true black. Negroid hair
is identical to Caucasoid and Mongoloid hair in amino-acid
composition and distribution (Khumalo and Dawber, 2005),
but has a larger diameter, lower water content, flattened
elliptical cross-section. It is usually black or dark brown,
tightly curled, low in shine when compared to Mongoloid
hair and high in sebum. It has increased grooming friction,
which combined with low tensile strength makes it more
difficult to manage.
HAIR GROOMING
Shampoos are detergents designed to remove sebum, sweat,
fungal elements, desquamated corneocytes, styling products,
and dirt. Conditioners are used to moisturize hair after
removal of sebum to leave the hair soft, smooth, hydrated,
and low in static. Many different shampoo detergents and
conditioning agents exist and are reviewed in detail else-
where (Draelos, 2005).
HAIR CARE
Modern cosmetic products are formulated to cleanse hair of
detritus, restore and improve cuticular and cortical function
and reduce detangling and grooming force. Intensive
conditioners containing poly-quaternium polymers,
dimethicones, and gum extracts are designed to obviate
the self-inflicted excesses of chemical and physical
damage. Intensive conditioning can temporarily ‘‘replace’’
the f-layer, improve moisture retention in the cortex
restoring some of the diminished physical properties of hair.
Improvement in hair shine is a key benefit of modern
products (Figure 4).
CONFLICT OF INTEREST
The author received an honorarium for consultant’s services from Procter &
Gamble towards the preparation of this article.
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Figure 4. Cosmetic products restore the optical and physical properties of
hair after weathering. 960  1458 mm (72  72 DPI).
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RD Sinclair
Healthy Hair

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