JOURNAL OF COSMETIC SCIENCE 18 The tresses were heat treated with ghd IV® straightening irons with 2-cm-wide ceramic plates at 175°–185°C (ghd UK, Silsden, West Yorkshire, UK). The tresses were wrapped in Post-It® paper at their root end, the lower edge of the Post-It® paper marking the top of the area to be heat treated. The tresses were treated with straightening irons for fi ve seconds. The irons were held in the same place throughout the treatment. Wet hair was put back into tap water for three minutes before being treated again. Each time, surface water was removed with tissue paper before applying the straightening irons. Dry hair was simply allowed to cool for three minutes before the start of another treatment. Treatments were repeated three times in each session, after which all the hair was put back into the dessicator for two days. In total, each tress was subjected to 4 × 3 treatments, which equates to a total treatment time of 60 seconds. Repeated fi ve-second heat treatments were selected for this study, as (a) they were realistic and (b) they made our measurements more sensitive to the effects of water, which evapo- rates very quickly. In reality, consumers and hair stylists quickly run straightening irons down each section of hair two to three times. Irons are, therefore, never in contact with any one part of the hair for more than a few seconds. A fi ve-second treatment time (with- out moving the irons down the switch) was selected to represent the heat exposure during one complete styling session. Long, extended treatment times, of, say, 5–30 minutes, as used by McMullen & Jachowicz (5), were not appropriate for our study. Longer heat treatment times are, perhaps, most suit- able for studying protein damage or testing the effectiveness of insulating materials. They are not suitable for investigating the effects of water, since the water evaporates within seconds. Treatment with straightening irons—single-dose experiments with “wet” and “dry” products. In single-dose experiments, 0.1 ml of product was applied to each tress before heat treat- ment. The tresses were wrapped with Post-It® paper, as described above, to clearly mark the area for heat treatment. The product was applied, from a syringe, to the top end of the exposed part of each tress (0.05 ml on each side) and spread downwards, just once, with the fi ngertips. The tresses were left to dry for two minutes before applying the straightening irons. The hair was treated with straightening irons for fi ve seconds. The irons were held in the same place throughout the treatment. After each heat treatment, the tresses were washed with shampoo (Charles Worthington Brilliant Shine® Shampoo, PZ Cussons (UK) Ltd, Stockport, Cheshire, UK). Shampooing followed a standard protocol. One milliliter of shampoo was applied to each tress. The shampoo was twice massaged into damp hair for 30 seconds, followed, each time, by 30 seconds rinsing under warm tap water. The cleaned tresses were air dried, and then put back into the dessicator. The treatments were repeated 12 times. Each tress, therefore, was heat treated, in total, for 60 seconds. Treatment with straightening irons—repeat dosing experiments with “wet” and “dry” products. In repeat dosing experiments, tresses were dosed and heat treated as above, but after cooling for one minute, the products were reapplied. This had the effect of building up the pro- tective layer created by the formulations. The tresses were dried for two minutes after the product was applied and then heat treated, again, for fi ve seconds. Product application and heat treatment were repeated three times before washing the tresses with shampoo. The cleaned tresses were air dried and then put back into the dessicator.

EFFECTS OF WATER ON HEAT-STYLING DAMAGE 19 The cycle of three repeat doses and associated heat treatments, followed by washing, was repeated four times. Each tress, therefore, was heat treated, in total, for 60 seconds. Fluorescence spectroscopy. Hair fl uorescence measurements were made using a computer-con- trolled fl uorescence spectrophotometer (Varian Cary Eclipse, Varian Inc., Palo Alto, CA). A solid sample holder accessory (Varian Inc.) was used to mount hair tresses in the instru- ment. The tresses were mounted horizontally at an angle of 30° to the axis perpendicular to the detector, with the root end closest to the detector. The angle at which switches were presented to the beam was found to be critical. Clipped hairs, cut 41 mm from the bindings (see above), were used to help position the beam over the center of the treated section of each tress (note: the treatment effects were invisible to the naked eye). The excitation beam was run at a visible wavelength and a wide-slit setting, to correctly po- sition the hair in front of the beam. In order to defi ne the optimum excitation wavelength, an excitation spectrum was run on virgin hair at a fi xed emission wavelength of 337 nm (Figure 1). The excitation spectrum showed a clear maximum at 285 nm, in good agreement with literature data on pure tryptophan (10). The fi nal settings used on all measurements were an excitation wave- length of 285 nm, a slit width of 2.5 nm, and an emission detector slit width of 10 nm. Spectra were measured from 300 to 550 nm at 4-nm intervals, with two seconds collec- tion time at each point. For the testing, spectra were taken fi rst from the treated parts of each switch. Control mea- surements were then made by moving the sample holder horizontally and taking an emis- sion spectrum from untreated hair further towards the root end of each tress. In this way, data were collected as a series of paired comparisons. Between each pair of measurements, the tresses were removed from the sample holder and turned over. This helped to randomize the effects of switch orientation and alignment across replicate measurements. Typical control and treated-hair measurements from the same switch are shown in Figure 2. The peak in fl uorescence at 328 nm, associated with tryptophan (5), is clearly visible in the control spectrum. A broad peak is also seen between 400 and 500 nm. This peak may be associated with keratin disulfi de bonds (5). Many spectra also showed a small sharp peak at 392 nm. The origin of this peak is unknown. Figure 3 illustrates how treat- ment with straightening irons reduces the intensity of the peak at 328 nm. The broad Figure 1. Excitation spectrum at a fi xed emission wavelength of 337nm. (Note: The signal at ∼340 nm is due to excitation/emission wavelengths coinciding and is not a fl uorescence feature of the hair.)