Hair is lifeless and desires 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, in addition to human hair discolor after sunlight exposure.
Human hair contains three melanin pigments. The primary 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 when they are absent, hair is vulnerable to static electricity, breaks with combing abrasion, and appears frizzy.
In order to understand Hair photoaging, it is essential first to grasp interaction between UV radiation with the hair proteins. Hair has an outer cuticle that gives protection for the inner cortex, which is composed of fibrillar proteins. These proteins are in command of the strength of the hair shaft. At the same time, melanin pigments are embedded in a protein matrix within the cortex. In this fashion, sunlight damages hair by physically making the shaft weak. Simultaneously, sunlight fosters oxymelanin production, leading to pigment reduction and lightening of hair color.
As regards topical exogenous hair photoprotection, it has not been different from skin photoprotection. Hair care products comparable to instant conditioners, styling gels, and hair sprays were added UV-B and UV-A sunscreens. However, this topical approach failed in creating a fair film that covers the whole surface area of each hair on the pinnacle. Moreover, it’s impossible because the entire surface area of hair on a human head is enormous. It might also be ideal that sunscreen sticks to the hair cuticle wrapping each hair in thickness, but without making the hair look oily.
Sunlight exposure results in 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 sort of hair photoprotection from oxidative damage.
If natural pigments provide hair photoprotection, then deposition of synthetic pigments on the cuticle and inside the cortex through hair dyes may protect hair shaft. There are two kinds of hair dyes: semipermanent and permanent.
Semi-permanent hair dyes are manufactured from a combination of dyes with the intention 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 within the hair shaft because 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 on account of the hydrogen peroxide and ammonia employed to make chemicals penetrate into the hair shaft. Regardless 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 increase the color of dyed hair. However, UV protection from shampoos is rather challenging for the reason that surfactant must be washed completely before styling.
Then again, conditioners can achieve a greater deposition of sunscreen on the hair shaft. Although not as effective as deep conditioners, which remain on the hair for 15 to half-hour; 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, similar to hair shaft roots or tips. Hair sprays have similar hair photoprotection effect since they are applied as a narrow film to a finished hairstyle.