UV Damage To Hair
Hair Composition
The hair is composed of non-soluble proteins called
keratins. Keratins have a high sulphur content and contain
a good balance of amino acids including cysteine, phenylalanine,
leucine, glutamine and lysine. Hair appearance contributes
largely to the overall facial image of a person, so
its condition can have aging effects.
Hair condition can deteriorate through three main
sources:
- mechanical - brushing, friction
- chemical - perms, oxidative colouring, lipid-depleting
surfactants
- environmental - solar radiation, hot-blow drying
heat, swimming pool chlorine.
Ultraviolet [UV] radiation is considered the most damaging
of all environmental factors. Radiation is responsible
for the photo oxidation of amino acids in the hair cuticle.
These amino acids play a key role in the stability of
hair protein. Photo damage of such amino acids [e.g.
cystine] leads to disulphide photo oxidation, destroying
the overall integrity of hair keratin.
The outermost layer of keratin fibres consist of approximately
three-quarters protein and a one-quarter lipid.
- UV degradation of amino acids results
in a fragmented keratin structure and significant
structural changes of the surface cuticle cells such
as lifting and thinning.
- UV-induced lipid degradation also
contributes to altered surface properties.
The state of the cuticle governs the frictional properties
of hair fibres and determines how the hair feels to
the touch and how it combs. UV induced physical changes
lead to a rough hair surface and higher forces will
be required to comb UV damaged hair.
UVA Versus UVB Damage
The two types of ultraviolet rays that damage hair
are Ultraviolet B [UVB] rays and Ultraviolet A [UVA]
rays. UVA rays, the longest rays and UVB rays, medium-wavelength
rays damage hair in a variety of ways.
UVB damages the cuticle - the outside covering of the
hair. Natural and chemical colors can fade and hair
can easily be dried out as a result of UVB rays. UVB
rays can also damage the hair fibers by penetrating
deep into the hair’s cortex and can damage the
hair cuticle.
UVA rays penetrate into the cortex and disturb the
hair cortex’s fiber-like cells that give the hair
its elasticity and strength, as well as damage the color
pigments that create natural hair color and burn the
hair cuticle.
Sun Damage On Hair
Hair has natural protection against the sun's rays,
but prolonged UV exposure causes major changes in the
mechanical ultra-structural and sensorial properties
of hair. Unlike the skin, hair does not signal burn
pain due to over-exposure. UV-induced damage is generally
only noticed after cumulative exposure starts to show
in telltale hair condition:
- change of texture
- dry appearance
- increase in porosity
- loss of suppleness.
These signs are directly related to the changing condition
and structure of the hair. All this damage causes dryness,
rough texture, split ends, susceptibility to breakage,
unmanageability, and loss of pigmentation and luster.
Dehydration - The sun strips the
hair of its natural oils and dry heat increases this
effect. UV rays attack your hair and the resulting free
radicals damage the hair. The weakened cuticle causes
the hair to become dehydrated, allowing bleaching and
fading of the color pigment as well as split ends.
Loss of Strength - UV damaged hair
sufferes loss of hair strength, increased difficulty
in combing and fading or loss of brilliance of hair
color, natural or added colour.
Keratin Breakdown - deep changes in
the structure of the keratin caused by the photo-oxidation
of amino acids, sterols and fatty acids in hair. It
results in rupture of disulfurated bridges, decomposition
of lipids, decrease in melanin (pigments of the hair)
as well as numerous micro-molecular lesions.
Loss of Color - Solar exposure alone
can lead to undesired results such as colour fading
[natural and artificial color] and loss in hair manageability.
The loss in manageability can be attributed directly
to an alteration of the hair surface. The hair encounters
more damage as it becomes more hypersensitive, the cuticles
of the hair surface are lifted and the hair shows more
split ends.
UV Damage On Treated Hair.
Protein makes up about 95% of a human hair. Perming
and dying the hair breaks disulfide bonds between protein
amino acids [hair strength] and alter the protein rich
internal structure of the fiber.
Permed hair - typically has only 90
percent of the original disulfide bonds, which leaves
hair weaker than before it was permed.
Permanent color - is altered by several
factors including humidity, sunlight, and other factors.
Sunlight is the most damaging to dye color.
Hair is an elastic solid, and can withstand normal
forces applied to it during combing and styling. However,
when hair color reduces the elasticity of hair the normal
tensile stress forces may exceed the lower maximum stress
[tensile strength] level, resulting in breakage.
UV Damage By Hair Type
The difference between damaged Caucasian hair [bleached
and permanently coloured] and virgin Asian hair is minimal;
both hair types are affected by treatment.
Dark melanin pigments [eumelanin] in virgin Asian
hair known to act as natural UV absorbers are mostly
found in the cortex of the hair and not in the cuticle.
This means that the proteins and lipids in the cuticle
of both hair types are equally sensitive to UV irradiation
and the damage resulting processes. The cuticle governs
the frictional properties of hair fibres, hence Asian
and Caucasian hair are equally affected in terms of
UV-induced loss of tensile strength.
Measuring UV Damage to Hair
UV damage to hair can be measured in a number of ways:.
- Fluorescence spectroscopy - damaged
hair shows up with less fluorescence intensity.
- Chemical reactive testing - reaction
with dansyl chloride. The fluorescent measurement
of dansylated hair can quantitatively assess certain
types of hair damages.
- Combability measurements - another
method to assess alteration of the hair cuticle due
to external stress and has proven to be a sensitive
tool to detect UV-induced hair damage
Studies
The effect of UV on hair has been confirmed by scientific
tests:
Reduce Color Fading
Tests showed conditioner only application reduced fading
by about 50% (maximum effect of 65% by Polysilicone-15)
Shampoo application by about 20% (maximum effect of
25% by both ABIL UV Quat 50 and Polyamide-2).
Shampoo AND rinse gave the maximum protection of 50%
reduced color change for the permanent coloration. Besides
this cationic silicone also Polyamide-2 performed well
in the shampoo application while Polyquaternium-59 provided
a good performance in the conditioner formulation.
Maintain Tensile Strength
Some UV-filters provided protection when used in a
conditioner formulation. The best was up to 40% less
reduction of the tensile strength change when using
either ABIL UV Quat 50 or Polyamide-2. The best protection
of the keratinous structure according to DSC measurement
was provided by both silicone derivatives, ABIL UV Quat
50 and Polysilicone-15.
Conclusion
The fastness of hair dyes and the degradation of the
hair fiber keratine can be protected against sun light
by using UV filters incorporated in shampoo or rinse
formulations.
Further studies are needed to achieve better UV hair
products, we need further understanding of the hair
structural changes caused by different radiation wavelengths.
We also need to clarify the effects of sun exposure
on different hair types; the amount and type of melanin
of each hair.
Related Pages
Protecting Hair
From UV Damage
UV
Hair Protection Products Ingredients
UV
Hair Protection Products
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