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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.