| 摘要: | 紫外線對皮膚造成紅斑、黑化及老化的現象，進而衍生SPF、PA及自由基等防禦參考指標。然而，頭髮是否也具此參考性指標？相關文獻指出[1]，頭髮照射太陽光能量達9´108 J/m2下（相當於日光中紫外線平均強度照射1100天），頭髮色澤中之亮度（L*）值方有明顯改變，但耗時太長。
有鑑於此，本研究利用以不同紫外光光源，對頭髮顏色造成之影響為主軸，將紫外線區分UVA（320~400nm）、UVB（280 ~320nm）及UVR註（280~400nm），分別照射特定能量，以色澤計（CIE Lab）觀察其色澤（DL*%、 Da*%、 Db*%、 （a*2+b*2）1/2及DE*）變化情形。另外使用頭髮拉力機，檢測頭髮個別受UVA 、 UVB及UVR，在特定能量照射後之拉力（屈服點、破壞點、延伸率及楊氏係數等）變化情形，來探討頭髮受特定能量紫外線照射後之影響。
結果顯示頭髮色澤，以光源UVR（280~400nm），在照射能量1.48´108J/m2下，色澤變化較明顯，（DL*%：3.89%、 Da*%：34.78 %、Db*%：63.46%、（a*2+b*2）1/2：1.78及DE*：0.97），其中以Db*%：63.46%差異最大。
而頭髮拉力部分，在照射紫外線能量1.48´108 J/m2下，UVA及UVB變化較不明顯，僅UVR在延伸率有降低（79.73%®31.80 %），故再持續照射UVA達1.75´108 J/m2（相當日照天數232天）及 UVB達2.32´ 107 J/m2 （相當日照天數345天），結果顯示屈服點及楊氏係數呈上升趨勢，而破壞點及延伸率，則呈現衰減；且有一明顯差異點發生在UVB能量1.85´107 J/m2 （相當日照天數
註:UVR(Ultraviolet Ray)=UVA+UVB
276天）（屈服點：10.03® 14.28，破壞點：20.39® 20.30，延伸率：59.33%®47.70%及楊氏係數dynes/cm2：3.22´1010® 4.64´ 1010）。使頭髮結構開始大幅度被UVB破壞（表4-4及5-4-2-2）。顯示頭髮結構中a-角質素之氫鍵、凡得瓦力、胜肽共價鍵、鹽基鍵及雙硫鍵，被紫外線UVB打斷；因而顯現頭髮易斷無彈性之性質（表4-3及5-2-4-1）。而UVA能量達1.75´108 J/m2 （相當日照天數232天） （屈服點kg/mm2：10.85® 13.76，破壞點kg/mm2：22.24® 19.95，延伸率%：59.33%® 54.40 %，及楊氏係數dynes/cm2：3.24´1010® 3.72´1010），變化仍不明顯。顯示頭髮結構物理特性，較不受單獨紫外線UVA所影響。
比較頭髮經紫外線照射後之色澤及拉力關係:
( a ) 紫外線UVB波長短能量大，可損害皮質層，打斷雙硫鍵，造成頭髮結構受損，並裂解麥拉寧色素，但又提供能量強化部分鍵結，使頭髮褪色變黃而脆；當照射能量達1.85´107 J/m2，延伸率及破壞點開始迅速衰減，顯示頭髮結構中大部份雙硫鍵，已被激發至極限，只要稍增加照射劑量，雙硫鍵即被瓦解。使頭髮物理特性，呈現彈性減弱且易斷現象。
( b ) 紫外線UVA波長長能量小，可穿透皮質層，破壞麥拉寧色素，造成頭髮色澤差異；但對頭髮結構較無傷害，使頭髮拉力之物理性質影響較小。
( c ) 紫外線UVR（UVA+UVB)，不僅打斷雙硫鍵，損害皮質層；還可穿透皮質層，破壞麥拉寧色素；對頭髮色澤及頭髮拉力結構，皆較個別之UVA及UVB 嚴重。顯示紫外線UVR中，除具有UVB的傷害外，同時亦有UVA能量提供，使得頭髮傷害加劇，而具有加乘效果。故紫外線UVR對黑色頭髮之損壞，大於個別紫外線UVB及紫外線UVA。
Since ultraviolet ray (UV) may cause erythema, tanning, and photoaging to the skin, various protection indices have been proposed, such as SPF (Sun protection factor), PA (protection grade of UVA) and free radical. However, whether hair has its own referential index is also an issue worth further investigation. Relevant literature[1] pointed that, it takes exposure dose of 9´108J/m2 in sunshine (equal to UV exposure dose of average intensity in the sun for 1100 days) to cause significant change in the luminance (L*) value of hair color; but a considerable period of the time is required.
Therefore, this research applied various UV light sources to examine their impacts on hair color. Divided into UVA(320~400nm), UVB(280 ~320nm), and UVR(a)(280~400nm), these ultraviolet rays were then given in specific doses. Afterwards, variation of color (DL*%[white-black], Da*%[red-green], Db*%[yellow-blue], (a*2+b*2)1/2, and DE*) was observed by colormeter (CIE Lab). Also, hair tension tester was applied to figure out changes in stretchability (yield point, break point, elongation rate, and Young’s modules) of hair under the influence of UVA, UVB, and UVR(a) respectively. The purpose was to understand the influence of UV exposure on hair.
The findings revealed that the most significant change in hair color occurred to Db*%(63.46%) under light source UVR(a)(280~400nm) with exposure dose of 1.48´108J/m2. Light sources in order of influence on the yellow-blue value of hair were: Δb*UVR > Δb*UVB > Δb*UVA.
As for hair stretchability, under the exposure dose of 1.48´108 J/m2, only UVR decreased elongation rate(79.73%®31.80%). So, further exposures to UVA of 1.75´108 J/m2(equivalent to sunshine duration of 232 days) and UVB of 2.32´ 107 J/m2 (equivalent to sunshine duration of 345 days) were given.
(a) UVR((Ultraviolet Ray)=UVA+UVB)
The result revealed a trend of increased yield point and Young’s modules, as well as decreased break point and elongation rate. Such powerful turning point was achieved at UVA exposure dose of 1.75´108 J/m2 (equivalent to sunshine duration of 232 days) with variations in yield point (10.85® 13.76 kg/mm2), break point (22.24® 19.95 kg/mm2) , elongation rate (59.33%® 54.40 %), and Young’s modules (：3.24´1010® 3.72´1010 dynes/cm2). The other is UVB exposure dose of 1.85´107 J/m2 (equivalent to sunshine duration of 276 days), causing variations in yield point (10.03®14.28 kg/mm2), break point (20.39®20.30 kg/mm2), elongation rate (59.33%®47.70%), and Young’s modules (3.22´1010 ® 4.64´1010 dynes/cm2).
These two energy points were the variation points where accumulated UVA and UVB destroyed, dissolved, or broke the bonds in hair structure, such as Hydrogen bounding, Van Der Waals forces, Peptide bond, Salt linkages, and disulfide bond of a-keratin.
Comparison between the hair before and after exposure to UV revealed the relationship between hair color and stretchability as follows:
(a) UVB that features in short wavelength and more energy can destroy cortex, break disulfide bond, and cause damages to hair structure. It can further crack melanin granules while providing energy to strengthen some bonds, making the hair turn yellow, brittle and breakable.
(b) UVA that features in long wavelength and less energy can penetrate cortex, damage melanin granules, and cause differences in hair color. But it’s less harmful to hair structure with less impact on hair’s physical property of stretchability.
(c) UVR which includes UVA and UVB may not only break disulfide bond, damage cortex, and even penetrate it to damage melanin granules; the impact on hair color and stretchability structure is more serious than that caused by UVA or UVB alone. |
