LIGHT RADIATION EFFECTS ON HAIR 675 Table V Effect of Ultraviolet Light on Virgin Hair Exposure Group Time No. (hr) Change in Total Radiation Yield Point a (langleys X 104) (%) Std. Dev. (+) 1 0 2 50 3 50 4 75 5 75 6 100 7 100 8 125 9 125 10 150 11 150 12 150 13 150 0 - 1.42 0.77 -4.03 0.77 -4.35 1.16 -5.47 1.16 -4.70 1.55 -7.16 1.55 -6.82 1.93 -7.64 1.93 -7.97 2.32 -10.2 2.32 -12.0 0 (shielded) -- 1.55 0 (shielded) -- 1.30 1.49 1.40 0.69 2.41 1.62 1.24 1.34 0.81 1.75 1.69 1.29 0.99 0.74 Average of 25 hair fibers per group. Table VI Effect of Ultraviolet Light on Bleach-Damaged Hair Change in Total Change in Yield Point Exposure Radiation Yield Point Net Changeb Group After Bleach" Time (langleys After Exposure in Yield No. (%) (hr) ( 104) (%) Point 1 --9.50 50 0.77 --13.8 --4.3 2 --9.05 100 1.55 --14.2 --5.2 3 --7.65 150 2.32 --18.4 --10.8 4 --8.88 150 2.32 --19.4 --10.5 Average of 25 hair fibers per group. Due to ultraviolet radiation. exponential relationship as shown in Fig. 4, i.e., as the radiation dose in- creased the effect on the tensile property became more pronounced. This behavior can be compared to that of severing individual strands ot: a yarn, wherein each successive rupture places a greater load on the remaining strands. A progression of this type would amplify the ten- sile effect as our test results indicate with radiation-induced disulfide rup- ture o[ hair keratin. The UV carbon-arc source in this experiment emitted 33.9 W/ft 2 of radiation below 400 nm or 20% of its total radiation compared to an average ot• 6.1 W/ft 2 or 5.9% ot• the total solar radiation in June. The

676 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS lOO •o 7o •o •o 1 .o 2.o 3.o Lo TOTAL RADIATION IN LANGLEYS, x10 -• Figure 4. Average change in yield point at 15% elongation as a function of total light radiation 4• Solar radiation data [] Ultraviolet light data greater UV intensity of the carbon-arc source, and its agTeements with the sunlight effects represented in Fig. 4, suggests the radiation effects on hair are independent of wavelength character but dependent upon the total absorbed radiation (19). This study along with other examinations into the photochemical reaction of hair and wool keratin (21-24) strongly suggests the important role of disulfide bonds in the light radiation effects on the tensile proper- ties of hair. While our in vitro measurements were centered upon the disulfide linkage and its effect on the tensile properties, there are other moleties that are sensitive to radiation. For example, the deamination or decarboxylation of amino acids (25), the disorientation of the hydrogen bonds, and the chemical alteration of the aromatic nuclei in tyrosine and phenylalanine (19). These additional factors must also be considered when attempts are made to ascertain the total effects of light radiation on the physical properties of human hair. ACKNOWLEDGMENT The authors wish to express their gratitude to Mrs. Tessie Wiegand for her meticulous and devoted work which has been a key to the suc-