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.
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.
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.
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.
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.
Carol Thopmson is doing research on Hair Ultraviolet Protection for quite some time. She has written a number of articles on Photodamaged Hair, and has shared her findings through TV talks.
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Ultraviolet Light Protection For Hair
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