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J. Cosmet. Sci., 60, 637–648 (November/December 2009) 637 Changes in structure and geometric properties of human hair by aging SHINOBU NAGASE, YOSHIO KAJIURA, AKIRA MAMADA, HIROKO ABE, SATOSHI SHIBUICHI, NAOKI SATOH, TAKASHI ITOU, YUYA SHINOHARA, and YOSHIYUKI AMEMIYA, Beauty Research Center, Kao Corporation, 2-1-3 Bunka, Sumida-ku, Tokyo 131-8501 (S.N., Y.K., A.M., H.A., S.S., N.S., T.I.), and Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561 (Y.S., Y.A.), Japan. Accepted for publication May 12, 2009. Synopsis To clarify hair changes by aging, the effect of age on hair properties was investigated from macro- to microscopic viewpoints. Sensory hair luster tests were performed on 230 Japanese females from 10 to 70 years of age, revealing that hair luster decreases with age. The age dependence of the hair diameter and the ellipticity of the hair cross section could not explain luster reduction by aging. It has been determined that an irregular increase in fi ber curvature occurs with age and is a cause of luster reduction with aging. A detailed structural analysis by synchrotron radiation microbeam X-ray diffraction revealed that the inhomogeneity in the lateral distribution of the hair microstructure increased with age and relates to the irregular increase in curvature. Such an increase in curvature is one of the important factors that leads to a poor alignment of hairs and luster reduction, and is related to the appearance of aging hair. INTRODUCTION Human hair undertakes important roles, such as protection of the head and displaying an attractive personal appearance. People, especially women, care for their hair day-to-day and have a deep interest in their hair. Most consumers are aware of, and try to minimize, undesirable changes in hair properties. One of the causes of the critical effects on hair properties is aging. The symptoms of aging appear everywhere in the body. Remarkably, they appear not only within the body, as in the decline in strength, but also in the skin. In the world of health care and cosmetics, a lot of research is aimed at anti-aging. However, studies of hair aging are relatively sparse. It is well known that hair grays and decreases in the number of fi bers, and the fi bers become fi ner with age (1–5). Several examinations reported that hair lipids are age-dependent and that some are related to the change from pre- to postmenopause (6–8). However, little is known about hair aging beyond these effects.