672 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table I Effect of Sunlight on Virgin Hair Total Radiation Change in Group (langleys Yield Point • No. Test Period X 104) (%) Std. Dev. (*) 1 9-26-68 to 12-4-68 2 9-26-68 to 12-4-68 3 2-6-69 to 4-17-69 4 4-17-69 to 6-27-69 5 7-1-69 to 9-9-69 6 7-1-69 to 9-9-69 7 4-20-70 to 6-29-70 8 4-20-70 to 6-29-70 9 4-20-70 to 6-29-70 10 4-20-70 to 6-29-70 11 6-29-70 to 9-8-70 12 6-29-70 to 9-8-70 13 6-29-70 to 9-8-70 14 9-8-70 to 11-17-70 15 9-8-70 to 11-17-70 16 9-8-70 to 11-17-70 17 11-24-70 to 2-2-71 18 11-24-70 to 2-2-71 19 11-24-70 to 2-2-71 1.60 1 6O 2 3O 3 53 3 6O 3 6O 3 31 3 31 3 31 Shielded 3.52 3.52 Shielded 1.76 1.76 Shielded 1.02 1.02 Shielded --958 --10 84 --16 9 --23 8 --32 7 --32 3 --27 8 --28.9 --29.9 --2.7 --45.1 --41.4 --3.0 --22.0 --21.5 --1.9 --7.3 --7.4 --0.76 2 4O 4 54 3 12 2 49 2 38 2 29 2.41 2.42 1.99 1.17 3.85 4.07 0.60 1.99 2.07 0.27 0.89 1.18 0.79 Average of 25 hair fibers per group. Table II Effect of Sunlight on Bleach-Damaged Hair Change in Total Change in Yield Point Radiation Yield Point Net Change Group After Bleach • (langleys After Exposure in Yield No. Test Period (%) X 104) (%) Point b (%) 1 9-26-68 to 12-4-68 --5.20 2 2-6-69 to 4-17-69 -5.50 3 7-1-69 to 9-9-69 -4.70 4 7-1-69 to 9-9-69 --4.40 5 4-20-70 to 6-29-70 --6.60 6 4-20-70 to 6-29-70 - 6.49 7 11-24-70 to 2-2-71 -6.19 8 11-24-70 to 2-2-71 --4.90 1 6O 2 3O 3 60 3 60 3 31 3 31 1 O2 I O2 --17.0 --11 --19.1 --13 --36.7 --32 --36.1 --31 --36.1 --29 --35.4 --28 --11.7 --5 --11.1 --6 Average of 25 hair fibers per group. Due to solar radiation. change in the yield point at 15% strain for each group was obtained as the difference between the yield point measurements taken before and after the exposure period. The standard deviation for each average is included.

LIGHT RADIATION EFFECTS ON HAIR 673 Table III Shielded Control Group Exposure Period: 6-29-70 to 9-8-70 Hair No. Yield Point at 15% Strain (g) 1st Test 2nd Test •o Change s 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 29.0 27.4 31.0 25.6 36.0 38.0 3O 0 3O 7 28 4 2O 3 28 6 33 2 29 3 29 5 32 3 37 6 37 4 25 2 28 1 32 9 36 0 28 7 35 9 35 0 34 5 27 8 26 7 30 0 24 9 34 9 36 7 29 1 30 0 27 5 19 9 27 8 32 3 28 7 28 7 31 2 36 1 36 2 24 6 27 1 32.2 35.0 27.6 34.9 33.8 33.7 --, .13 --2 55 --3 22 --2 73 -- 05 --3 42 --3 00 --2 28 --3 16 --1 97 --2 79 --2 71 --2.04 --2.71 --3.40 --3.98 --3.20 --2.38 --3.55 --2.12 --2.77 --3.83 --2.78 --3.42 --2.31 Average, --2.95% std. dev., -v0.60. These yield point data indicate the tensile effect of summer solar radiation to be five times greater than that which was experienced during the winter months. While the differences in the seasonal radiation levels were expected, the pronounced tensile alteration and the effect on the disulfide linkages in the hair keratin were not anticipated. The shielded sample groups experienced minimal changes during the test period and were probably due to residual infrared scattering or thermal radiation. The bleach-damaged hair, with fewer disulfide linkages (17), was included in this study to determine whether or not the additional radiation damage was additive or potentJared. These results indicate an additive effect at these low levels of bleach damage. The data in Tables III and IV illus- trate the yield point measurements, as grams of force at 15% strain, of an exposed and shielded sample group of hair from a summer test.