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Although hair is lifeless and needs no protection from ultraviolet
(UV) radiation because hair shaft carcinogenesis is not feasible;
and although damaged hair can be removed and replaced by new growth;
hair photoprotection plays a significant role in preserving hair
shaft for the sake of cosmetic worth, especially appearance problems.
Much like natural fiber, natural unprocessed human hair undergoes
photoyellowing, a chemical process by which wool, cotton, or silk,
as well as human hair discolor after sunlight exposure.
Human hair contains three melanin pigments. The first two, eumelanin
and pheomelanin, account for the brown and red hues found in hair
respectively. The third pigment, oxymelanin, is found after unprocessed
hair has been exposed to sunlight. This melanin reduces the cosmetic
value of the hair as well as affecting hair dye and perm.
UV radiation also affects hair lipids, making photodamaged hair
dull and dry. Hair lipids wrap the hair shaft conferring gloss
and manageability, but if they are absent, hair is vulnerable
to static electricity, breaks with combing abrasion, and looks
frizzy.
In order to comprehend hair photoaging, it is essential first
to understand interaction between UV radiation with the hair proteins.
Hair has an outer cuticle that provides protection for the inner
cortex, which is composed of fibrillar proteins. These proteins
are in charge of the strength of the hair shaft. At the same time,
melanin pigments are embedded in a protein matrix in the cortex.
In this way, sunlight damages hair by physically making the shaft
weak. Simultaneously, sunlight fosters oxymelanin production,
resulting in pigment reduction and lightening of hair color. Since
the only endogenous hair photoprotection comes from the pigments
within the hair shaft, these produce chemical changes to protect
the protein structure, but with an alteration in the hair color
as a result.
As regards topical exogenous hair photoprotection, it has not
been different from skin photoprotection. Hair care products such
as instant conditioners, styling gels, and hair sprays were added
UV-B and UV-A sunscreens. However, this topical approach failed
in creating an even film that covers the whole surface area of
every hair on the head. Moreover, it is impossible because the
total surface area of hair on a human head is enormous. It would
also be ideal that sunscreen sticks to the hair cuticle wrapping
each hair in thickness, but without making the hair look oily.
This challenge has resulted in cosmetic researchers to think about
hair photoprotection through the internal structure of the hair.
Sunlight exposure leads to lightening of the hair color and,
eventually, fiber damage. However, it has been proven that unpigmented
hair is more vulnerable to UV damage than pigmented hair, indicating
that color granules provide some kind of hair photoprotection
from oxidative damage.
If natural pigments provide hair photoprotection, then deposition
of synthetic pigments on the cuticle and within the cortex through
hair dyes may protect hair shaft. There are two kinds of hair
dyes: semipermanent and permanent.
Semi-permanent hair dyes are made of a combination of dyes in
order to arrive at the final desired color. These are left on
the hair for 25 minutes approximately. Although dyeing damage
hair fibers, the damage is outbalanced by antioxidant effect of
the color deposited on and in the hair shaft as the hair is exposed
to UV radiation. The darker the hair dye color, the more hair
photoprotection provided.
Permanent hair dyes penetrate deeper into the hair shaft. Although
they act as hair photoprotection agents as well, they cause more
damage as a result of the hydrogen peroxide and ammonia employed
to make chemicals penetrate into the hair shaft. In spite of producing
more cuticle and hair shaft structure damage, alkaline dyes provide
better hair photoprotection since they reduce hair fiber protein
damage, acting as passive photo filters.
As well as hair dyes, there are other hair products that can
act as hair photoprotection agents, among which we found shampoos,
instant conditioners, deep conditioners, and hairstyling products.
Some shampoos intended for dyed hair include sunscreens. They
are designed to extend the color of dyed hair. However, UV protection
from shampoos is rather challenging since the surfactant should
be washed completely before styling.
On the other hand, conditioners can achieve a better deposition
of sunscreen on the hair shaft. Although not as effective as deep
conditioners, which remain on the hair for 15 to 30 minutes; instant
conditioners are applied after shampoos and washed before towel
drying. In fact, the contact time of the conditioners containing
sunscreen with the hair establishes the level of hair photoprotection.
The longer, the better.
Probably the best UV protection products are styling products
that are administered after hair drying and among which are blow-drying
conditioners, styling gels, and hair sprays. Blow-drying conditioners
are applied through massaging the wet hair before drying. Styling
gels may not provide as much protection when applied only to certain
areas of the hair, such as hair shaft roots or tips. Hair sprays
have similar hair photoprotection effect since they are applied
as a narrow film to a finished hairstyle.
Although a myriad of UV protection products exist for hair photoprotection,
the best way of UV protection would still be the use of hats,
scarves, or umbrellas.
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