Hair, sun, regulation, and beauty
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Post on 29-Mar-2017
Journal of Cosmetic Dermatology, 13, 1--2Hair, sun, regulation, and beautyZoe Diana Draelos, MDThe recent sunscreen guidance issued by the US FDAprohibited the use of SPF ratings on hair-care products,even though these products may contain photoprotec-tive ingredients listed on the sunscreen monograph.The US FDA has also questioned the adequacy ofphotoprotection provided by spray on sunscreens.These concerns are understandable based on the dis-continuous film created by spray on products. It is esti-mated in clinical testing that the SPF on the packagingcan only be achieved if the spray sunscreen is appliedfollowing by rubbing three consecutive times. Whilethis is possible on skin, it is not possible on hair. Spraysunscreens for the hair cannot possibly evenly coatevery square inch of the hair shaft. It also doubtfulhow much sun protection is provided by shampoosand rinse away instant conditioners that contain sun-screen. The short contact time followed by abundantwater rinsing may remove any photoprotection. Thisthen begs the question as to whether nonliving hairshafts really need sun protection at all. The answer ismost emphatically yes, and I will proceed to explainthis important cosmetic need.As hair is nonliving, it cannot be sunburned orundergo photocarcinogenesis; however, UV and visibleradiation are very damaging to the cosmetic value ofthe hair. Much of the current understanding of hairphotodamage comes from textile research on wool.Natural fibers, such as wool, cotton, silk, and rayon,discolor when exposed to sunlight. White fabrics tendto take on a light brown/yellow color, a process knownas photoyellowing. In natural human hair, there aretwo pigments, eumelanin and pheomelanin, account-ing for the brown and red hues seen in hair,respectively. There is another melanin, known as oxy-melanin, found in unprocessed human hair that hasbeen exposed to sunlight. Oxymelanin is an oxidativephotodegradation product.1Lighter-colored hair, such as blonde hair, is moresusceptible to hair photodamage than deeply pig-mented hair, such as brown hair. Black hair begins tolighten in color after 300 h of exposure to simulatedsunlight, while blonde hair begins to yellow after300 h of exposure to simulated sunlight and begins tolighten when exposed to 3001200 h of simulatedsunlight exposure. The hair color lightening or bleach-ing is primarily due to the effects of visible light. How-ever, not only does the hair change color, but it alsoexperiences a 200300% increase in friction, indicat-ing damage to the proteins in the cuticle.The hair protein that is mainly damaged by sunlightis cystine, which is oxidized to cysteic acid. It is thesulfur-containing amino acids that are most sensitiveto oxidative damage, and of course, it is the sulfur-con-taining amino acids that give the hair its structuralstrength. Other amino acids, such as tryptophan andtyrosine, are also degraded by light. After 150 h of sunexposure, blonde hair shows a 2530% decrease intryptophan, 25% decrease in cystine, and 80%decrease in tyrosine. As oxidation occurs, there is acompensatory 80% increase in cysteic acid. Thesesame changes are also seen in black hair, but at least300 h of sun exposure was required to produce thesame oxidative damage.2Sunlight also decreases the tensile strength of thehair fiber. This means that when the hair is combedand stretched, it is more likely to break. This effect ismagnified with age as the diameter of the hair shaftdecreases in both men and women. The diameter offemale hair shaft increases up to age 35 and thendecreased gradually after age 40 with further decreasesafter menopause. In men, the diameter of the hairshaft decreases after puberty.The natural photoprotection in hair is melanin, whichalso provides endogenous photoprotection in the skin.Melanin is broken down by visible and UV radiation inthe hair shaft giving rise to a phenomenon known asphotobleaching. This phenomenon is especially pro-nounced in blonde hair, which lightens dramatically inthe summer, but also results in permanent changes inthe hair shaft internal amino acids and external lipids.Unpigmented hair, such as gray and white hair, ismore susceptible to UV damage than pigmented hair.3Also, the rate of cystine disulfide bond breakage isgreater for unpigmented than pigmented hair. Thismeans that one of the best sources of photoprotectionis hair dye. 2014 Wiley Periodicals, Inc. 1Editorial EchoesWhite unpigmented hair looses more mechanicalstrength after 4 days of UV radiation than semiper-manently dyed brown hair. This same effect is alsopresent with permanent hair dyes. The permanenthair dye acts as a passive photofilter reducing thehair fiber protein damage by attenuating the incidentlight. The dye molecule absorbs the light energy,which promotes it to a more excited stated, followedby a return to ground state via radiative and nonra-diative pathways. As might be expected, the darkerthe hair color the more photoprotection imparted bythe dye.SPF rated sunscreens to promote hair beauty andhealth probably will not be forthcoming in light of thenew sunscreen guidance. Indeed, consumers mightmisinterpret sunscreen-containing hair products andmistakenly think that if the shampoo runs over thebody, adequate sunscreen might be left behind. Yet,there is a need within current regulation to addressthe fact that sun exposure is detrimental to hairbeauty. Consumers seem much more pre-occupied withhaving a good hair day than wearing sunscreen ontheir face and bodies to insure a good skin day.Perhaps cross-education from sunscreen-containinghair-care products might spill over into proper skinsunscreen application, especially in impressionable ado-lescents. It is also worthwhile to give consumers anidea of how much photoprotection they are gettingfrom hair-care products to maintain hair beauty. Withnew sunscreen technology, it may be time to create aseparate hair sun protection scale to make consumersaware of how to more effectively beautify their hair.Who knows, it might be enough to encourage arenewed interest in skin photoprotection!References1 Hoting E, Zimmerman M. Sunlight-induced modificationsin bleached, permed, or dyed human hair. J Soc CosmetChem 1997; 48: 7991.2 Gonzenbach H, Johncock W, De Polo KF et al. UV damageon human hair. Cosmet Toilet 1998; 113: 439.3 Tolgyesi E. Weathering of hair. Cosmet Toilet 1983; 98:2933.2 2014 Wiley Periodicals, Inc.Editorial Echoes
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