J. Cosmet. Sci., 62, 15–27 (January/February 2011) 15 The effects of water on heat-styling damage PAUL CHRISTIAN, NIGEL WINSEY, MARIE WHATMOUGH, and PAUL A. CORNWELL, School of Chemistry, The University of Manchester, Oxford Road, Manchester, UK, M13 9PL Mar-Tech Contract Services Inc., 888 Sussex Boulevard, Broomall, PA 19008 and PZ Cussons (UK) Ltd, Innovation Centre IC-H, Agecroft Commercial Park, Lamplight Way, Manchester, UK, M27 8UJ. Accepted for publication September 8, 2010. Synopsis Heated styling appliances, such as straightening irons, have grown in popularity in recent years, as have hair products such as heat-protection sprays. In this study we investigate whether the water in a heat-protection spray can affect the level of damage caused by heat styling. Tryptophan damage from heat styling was measured using fl uorescence spectroscopy, and structural damage was investigated using light microscopy and single-fi ber tensile testing. Hair samples were heat treated with straightening irons, following treatment with either a water-based, “wet,” heat-protection spray or an etha- nol-based, “dry,” spray. Results showed that, as expected, tryptophan damage was reduced by repeated applications of both the “wet” and “dry” heat-protection sprays. However, no differences were seen between the “wet” versus the “dry” product. Light microscopy studies showed greater structural damage to hair treated with water and the “wet” spray. Tensile tests confi rmed that there was greater damage to hair treated with the “wet” spray. Decreases in Young’s modulus were greater in the presence of the “wet” spray. The results of this study suggest that the type of damage caused by heat treatments is different in wet versus dry hair. In dry hair, thermal treatments cause chemical damage and some structural damage. However, in wet hair, thermal treatments cause the same chemical damage, but considerably more structural damage, which causes signifi cant changes in the physical properties of the hair. It is likely that the rapid evaporation of water from the hair is the main causal factor. Our experiments suggest that the effectiveness of commercial heat-protection sprays can be improved by the removal of water and by the use of volatile ingredients, such as ethanol, as base solvents. INTRODUCTION Styling hair with straightening irons or curling tongs to achieve smoother, straighter hair styles, or curls and waves, has grown in popularity. In the UK, for example, over a third of women currently use straighteners every time they wash and style their hair (1). Straightening irons and curling tongs are usually used after blow-drying, and act to drive out any remaining water in the hair. The removal of water encourages the formation of more bonds between hair proteins, helping to set the hair in its new conformation.
JOURNAL OF COSMETIC SCIENCE 16 The popularity of straightening irons and curling tongs has created a large market for hair products associated with heat styling. These include heat-protection sprays, straight- ening balms, curl creams, and heat-protection shampoos and conditioners. Heat-protec- tion sprays are very popular. In fact, heat-protection sprays are now the second most frequently used type of styling products used in the UK, second only to hairsprays (1). Heat-protection sprays are usually designed to protect the hair from heat damage, and to give some conditioning and style hold. They are usually sprayed on to the hair after blow- drying and immediately before applying the straightening irons or curling tongs. The plates of straightening irons and curling tongs reach a range of different tempera- tures. Ghd IV® straightening irons, for example, claim to reach 185°C, and other irons claim to reach temperatures of up to 230°C. At these temperatures there is always going to be some damage to the hair. It is well known that heat-styling damage from blow- drying and hot irons can be both physical and chemical in nature. Cycles of wetting and blow-drying hair can result in the formation of multiple, “axial” cracks in the cuticles, aligned parallel to the longitudinal axis of the hair fi ber (2). These axial cracks form when the external portions of hair fi bers undergo rapid dehydration. Cycles of wetting and blow-drying have also been found to produce deep ovoidal (or bubble) cuticle cracks (3). These cracks are attributed to a combination of cyclic extension actions and the rapid escape of water while drying. Heat treatment with curling irons has also been shown to produce radial and axial cracking along with scale edge fusion (4). Bubbling and buckling of the cuticle was also observed (4). The chemical effects of thermal treatments (such as treatment with curling tongs) on human hair were investigated by McMullen and Jachowicz (5). Their work demonstrated that heat treatments of between 130° and 164°C result in a decomposition of chromo- phores, specifi cally tryptophan and its oxidation products (kynurenines), and an increase in the yellowness of white hair or a simultaneous yellowing and darkening of bleached hair. In other studies, curling irons have also been shown to lower the dynamic contact angle of the hair surface as cuticle lipids are damaged and removed (6). The effects of structural and chemical damage to the physical properties of the hair in- clude increased hair breakage on combing (7) and, in severe cases, acquired trichorrhexis nodosa (brittle hair) (8). Increases in combing forces are also observed (5), particularly in hair subjected to repeated heat treatments separated by rinsing. A number of ingredients have been investigated as insulators against heat-styling dam- age. These include sodium polystyrene sulfonate (6), quaternium-70 and polyquater- nium-11 (9), PVP/DMAPA acrylates copolymer (9), sodium PEG-40 maleate/styrene sulfonate copolymer, and silicone quaternium-22 PPG-myrisyl ether. Some other humec- tant-type ingredients, such as hydrolyzed wheat protein, have also been shown to reduce damage (9). Most heat-protection sprays on the market at present use these kinds of technologies to protect the hair. However, they all, at present, are formulated as water or water/ethanol- based products. Since some studies (4) have suggested that the structural damage caused by curling irons is greater on wet hair than on dry hair, we have decided to investigate the benefi ts of using a water-free heat-protection spray made with a volatile solvent such as ethanol. We hypothesize that less chemical and structural degradation should occur at high temperatures in hair treated with a “dry” spray versus hair treated with a “wet” spray.
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