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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:

  1. mechanical - brushing, friction
  2. chemical - perms, oxidative colouring, lipid-depleting surfactants
  3. 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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