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J. Cosmet. Sci., 63, 233–241 ( July/August 2012) 233 Trehalose in hair care: Heat styling benefi ts at high humidity SUSAN PYE and PREM K. C. PAUL Unilever R&D, Portsunlight, Wirral, UK, CH63 3JW. Accepted for publication November 18, 2011. Synopsis Human hair switches that have been treated with trehalose solution and straightened using hot irons show longevity of the straight style even in high-humidity conditions. This anti-humidity benefi t is especially notice- able if the straight style has been created at low relative humidity. It is proposed that hot-iron straightening of trehalose-treated switches produces in situ glassy forms of the sugar that act as water sinks at high humidity to provide anti-humidity benefi ts. Adsorption isotherms and powder x-ray studies of different forms of trehalose and moisture uptake of hair treated with the sugar suggest that the ability of a glassy form of trehalose to regulate moisture in the fi ber and consequently affect its viscoelastic properties is a major factor in providing long-lasting straight style in humid conditions. INTRODUCTION In the last few years with the advent of ever more sophisticated appliances and hair care products, it has become far easier to create desired hair styles. While in ambient conditions styles last for a few hours, at high humidity hair style loss is accelerated and consumer satis- faction recedes in only a matter of minutes. The retention of hair styles for a longer period, especially at high humidity, is therefore a big and hitherto unmet consumer need. Trehalose, a naturally occurring osmolyte, is a non-reducing disaccharide formed by the 1→1 linkage of two D-glucose residues. Cells of many organisms, including bacteria, yeast, fungi, insects, invertebrates and plants, use trehalose to protect their proteins and biological membranes against extreme dehydration, desiccation, temperatures, and many unfavorable environmental conditions (1–8). For this reason trehalose is increasingly fi nding uses in med- icine, pharmacy, food processing, and personal care products (9). Typical applications include trehalose as a stabilizer of proteins and as an excipient in pharmaceutical formulations. In hair care, trehalose has found increasing use in the benefi t areas of damage repair and style manageability (10). Here we look at the effect of trehalose in heat-styling benefi ts, particularly in providing style maintenance benefi ts in high-humidity conditions. Address all correspondence to Prem K. C. Paul at prem.paul@unilever.com.