Susan Daly

Fluorescence and coloration of grey hair.

Grey hair samples were collected from 11 individuals and separated into un‐pigmented and pigmented fibres (International Hair Importers). Fluorescence measurements were obtained by using a double‐grating fluorescence spectrophotometer and a bifurcated fibre optics accessory to measure the spectra directly from the surface of hair at various distances from the fibre root. Colour measurements were carried out by using a Hunter colorimeter. The fluorescence spectra of un‐pigmented hair obtained by the excitation at 290 nm show a peak at 356 nm [tryptophan (Trp)], and multi‐peak emissions in the range from 395 to 500 nm. A significant variation in the Trp emission intensity at 356 nm vs. the intensity of emission in the 395–500 nm range was observed for hair collected from various individuals with yellow coloured hair producing stronger relative emission in 395–500 nm range. Quantitative measurements of coloration and the calculation of the Yellowness Index (YI) showed linear correlation between YI and the ratio of fluorescence intensities I440/I356 The spectra obtained by excitation at 320 nm showed the emission peaks at 395 nm (unidentified), 420 nm (N‐formylkynurenine), 460 nm (kynurenine), and 495 nm (3‐hydroxykynurenine), which are the products of oxidative or metabolic conversion of tryptophan. Un‐pigmented, yellow hair showed a build‐up of the fluorescence band corresponding to 3‐hydroxykynurenine at 495 nm. The data also showed the fluorescence quenching effect of melanin resulting in the lowering of the fluorescence intensity of pigmented hair. The spectra obtained at various positions along the fibres demonstrated gradual photo‐decomposition of hair chromophores during their lifetimes. This was indicated by a decrease of Trp fluorescence intensity, which was relatively fast (8·10−4–1.5·10−3 [day−1] as calculated for hair obtained from various individuals) for un‐pigmented hair and slower for pigmented hair. A decrease in Trp emission was accompanied by an increase in the yellow coloration toward the ends of un‐pigmented fibres.

Grey hair: clinical investigation into changes in hair fibres with loss of pigmentation in a photoprotected population

Loss of pigmentation in hair fibres is one of the most obvious phenotypic changes with ageing and has been a topic of increasing interest in the study of follicle biology. The onset of greying brings cosmetic complaints that grey fibres are wild or difficult to manage. Of course, these perceptions may be the consequence of visual obviousness rather than underlying physical or chemical differences. Although several studies have compared pigmented and unpigmented fibres, few have tried to control genetic and ethnic difference as well as extrinsic factors such as photoexposure and chemical treatment. We have recruited subjects with salt‐and‐pepper hair from a population of Old Order Mennonites who, for cultural reasons, are not only prohibited from chemically treating their hair but also limit their exposure to sunlight. Hair samples were examined for elemental composition, surface energy, Young’s modulus, break stress, bending modulus, shear modulus and water sorption/desorption isotherm. The parameters were evaluated statistically for global differences, individual differences and typical individual differences. Consistent with previous published literature, few global differences were found between pigmented and unpigmented hair across the population. We do find that many individual subjects had differences between pigmented and unpigmented fibres. These differences tend to be more pronounced in bulk than in surface properties. The small differences in mechanical properties and moisture uptake and loss lend support to the perception by consumers that grey hair is wilder, drier and less manageable.

Chemistry of Sunscreens

Sun filters can be classified as organic, organic particulates, polymeric, and inorganic particulates.