EFFECT OF UV RADIATION ON HAIR STRUCTURE 103 Table IV Summary of Solar Light Irradiation Energy and Power, and Exposure Time and Humidity Used by Several Authors in Their Studies (some quantities were derived to SI units from the quantities reported in the articles). Wavelength Spectral Irradiance range or Reference (nm) Irradiation Energy 300-315 0.7 Wm- 2 nm- 1 Solar radiation 315-380 0.5 - 1.2 Wm-2 nm- 1 Cleveland , OH, June 1986 380-700 1.2 - 1.9 Wm-2nm- 1 IQ-Panel) 300-400 74.6 Wm-2 Spectral Global Solar Irradiance 400-800 604.2 Wm-2 ASTM G151 Renewable Resource Data Center, National Renewable Energy Laboratory UV-VIS-IR 10 106 - 20 106 J m-2day- 1 and Bureau of Meteorology of Australia (Data available on the internet) 6,330 X 106 J m-2year -1 UV-VIS-IR = 520 X 106 J m-2month -1 = 17.3 X 106 J m-2day-1 Q-P anel = 300 x 106 J m-2 year-I (Actual data for Florida, an average of UV = 25 x 106 J m-2month- 1 3 years) = 0,82 x 106 J m-2day- 1 52 % of the total energy is VIS: (Personal Communication) VIS = 3,300 x 106 J m·2 year-I = 270 106 J m-2month-I = 8.9 106 J m-2 day-I IRRADIATION PARAMETERS USED BY THE DIFFERENT AUTHORS Wavelength Spectral Irradiation Source of range Irradiance Energy radiation Comments (nm) (Wm-2) 8 X 104 - Solar (Dubief) Up to 3 months (natural light). 18 x 104 J cm-2 radiations, Up to 360 hr (15 days, 1.3 x 106 s) of UV- VIS 615 - Suntest and exposure to artificial light. 1,384 (8 X 108 - Xenon test Suntest: 40° C, 3-7 % RH 1.8 X 109 J m-2) Xenotest: 25° C, 88% RH 280-350 UVB 2.5 9 X 106 J m-2 320-400 UVA 48 1.8 X 108 J m-2 (Hoting) Total irradiation time 1,008 hr 370-780 VIS 463 1.6 X 109 J m·2 Lamp + filters (= 3.62 x 106 s), 25-48° C at 22-94 % 750-2,800 IR 440 1.6 X 109 J m-2 R.H. 280-1,100 1,037 3.7 X 109 J m-2 Global 300-400 50.6 = 127 X 106 QUV solar (Rutsch) Up to 700 hr exposure (2.52 x UV Jm-2 simulator 106 s), 10-95 % RH, 40°-50° C. 300-400 44.6 = 112 X 106 AW solar Oxidative post treatments and water UV Jm-2 simulator immersion post-treatments. 300-700 412.7 = 104 X 107 (UV+VIS) Accelerated weather testing UV + VIS Jm-2 Atlas weather-Ometer 280-320 UVB 1.4 2.42 X 106 (Gao) 20 days (1.73 x 106 sec), 2T C, 65 Jm-2 Different lamps % RH, treatment repeated every 24 hr. 320-400 UVA 4.9 8.47 X 106 were combined Jm-2 Daylight 139 X 106- Atlas Ci35A (Pantle) 96 hr-226 hr (=9 days), so· C, simulator 178-401 312 X 106 J m·2 50% RH. UV +VIS (up to 0.813 x 106 sec) Daylight Heraeus (Bernhard) Up to 30 days, 50% RH, 25'- simulator 41.3 107 X 106 J m·2 Xenon Test 45' C. 5% Solids of different UV filters. UV+VIS (Up to2.59 x 106 sec) UVB 2.77 107 J m·2 UVB lamo (!novel 100 hr irradiation time Ir is important to note that an equivalence in the energy that the sun is radiating and that of a solar simulator does not necessarily reflect a true correspondence in terms of the effect on the substrate (hair) properties.

104 JOURNAL OF COSMETIC SCIENCE pigment granules appeared intact. However, when the same pigmented (and previ­ ously UV-exposed) hair fibers were treated with alkaline hydrogen peroxide, melanin was instantaneously disintegrated, revealing that severe damage was produced by the UV irradiation to both keratin and melanin. 5. Water and humidity are believed to have a very crucial role in the decomposition of the protein structure and in the mechanism of photobleaching. High RH accelerates photochemical oxidation of hair and is the primary contributing factor to accelerated loss in hair color (melanin). The findings in this paper indicate that prolonged UV irradiation can have a devastat­ ing effect on human hair. Also, it is crucial to introduce high-humidity or better shampoo/cleansing/water immersion cycles into the protocol of exposure of hair to UV /VIS radiation to induce some of the changes that would not otherwise been ob­ served. In 1993 Pande and Jachowicz published a paper in which the amino acid tryptophan (Trp) is identified as an early indicator of photodamage in human hair (13). Trp is an integral part of keratin and it absorbs UV rays at a maximum wavelength of 280 nm. The study shows that both simulated light (irradiation wavelength 295 nm) and sunlight (summer in Connecticut, total exposure length 72 hr) can damage Trp, resulting in the depletion of its fluorescence emission. The effect of water versus min­ eral oil was also explored the experimental procedure employed appears to give more accurate results when the fibers are soaked in a medium. While no great differ­ ence was found between wet or dry fiberse exposed to UV radiation, a big difference was found between water-soaked fibers and fibers soaked in mineral oil. The rate of destruction of Trp was found to be much lower in non-polar media (mineral oil) than in water. The study hypothesizes on the kinetics of photodegradation, proposing that the photo­ degradation of Trp precedes that of the disulphide bond in keratin, where significant loss in Trp is detected before any increase in photo-oxidation products is detected. UV­ weathered hair appears to be characterized by a lower Trp, but by a higher cysteic acid concentration. This paper describes a unique approach to the investigation of photodam­ age, very specific to one amino acid. Some effort was made to correlate natural light to the radiation emitted by the solar simulator however, this comparison was not very comprehensive. More recently, Inoue et al. (14) reported that a type of protein, classified as Sl003A (high cystein content protein) and found predominantly in the cuticular region (endo­ cuticle), is thought to be intimately involved in the disulphide bond cross-links that determine the structural integrity of hair fibers. This study shows that irradia­ tion of hair with UV radiation induces damage to the S 1003A disulphide bonds that link the protein to the rest of the hair matrix, resulting in the ability to elute the protein from the hair fiber. UV irradiation was performed using a UVB lamp (100 hr, 10 J cm- 2 hr). A four-stage model was proposed where the elution of S 1 00A3 is the major cause of hair damage. The authors conclude that UV radiation, as e Dry hair fibers gave more background noise and less contact area with the sample holder cell. Possibly because of lesser accuracy, no significant difference was found between irradiated dry and irradiated wet hair fibers, in terms of Trp content.