J. Cosmet. Sci., 69, 347–356 (September/October 2018) 347 Role of Internal Lipids in Hair Health JENNIFER M. MARSH, SHANE WHITAKER, TIM FELTS, WILLIAM SHEAROUSE, MIKE VATTER, ARTO MÄÄTTÄ, MATTHEW THOMPSON, and TIMOTHY J. HAWKINS, The Procter & Gamble Company, Mason Business Center, Mason, Ohio ( J.M.M., S.W., T.F., M.V.), The Procter & Gamble Company, Ivorydale Technical Center, Cincinnati, Ohio (W.S.), Department of Biosciences, Durham University, Durham DH1 3DT, UK (A.M., M.T., T.J.H.) Synopsis Saturated and unsaturated fatty acids make up 85% of the total hair lipid content and are found in the cuticle and cortical cell membrane complex. Although these lipids only make up 2–6% of the hair’s overall weight, they play a crucial role in keeping hair healthy, infl uencing shine, feel, manageability, and strength. The objective of this work was to understand the mechanisms of how these lipids are lost on exposure to external stressors, such as chemical treatments, washing, and UV exposure and to understand how their loss impacts hair strength. The experimental approach was to measure these lipids and oxidation products, lipid peroxides (LPOs) and correlate their loss with fatigue strength measurements. The results show lipids are lost over time by washing, exposure to chemical treatments, such as coloring, and environmental insults, such as UV, and it was confi rmed that a mechanism of degradation is via oxidation of unsaturated lipids to form LPOs. In addition, it was shown that replenishment of these lipids is possible by incorporating lipids, such as fatty alcohols (FaOHs), into a gel network with anionic surfactants to create a delivery system that can effi ciently penetrate FaOHs into hair and increase internal strength as measured by fatigue. INTRODUCTION Hair health is an important attribute to consumers and, thus, to the cosmetics industry. Reducing the signs of damage, such as poor shine and manageability, split ends, broken fi bers, and poor feel are targets for many products in the hair care regimen, especially sham- poos, conditioners, and treatments. Thus, it is important to understand the underlying causes of hair structural damage from external stressors to develop better performing prod- ucts. These stressors include chemical treatments, such as coloring, perming, and relaxing, UV exposure, excessive heat exposure, and physical abrasion from washing and combing. As we consider hair changes we need to investigate all the major components of hair, the cuticle, cortex, medulla, protein, and lipid structures. Of interest in this study are the Address all correspondence to Jennifer M. Marsh at marsh.jm@pg.com.

JOURNAL OF COSMETIC SCIENCE 348 lipid components of hair, which play a major role in the structural integrity of hair. Spe- cifi cally of interest are internal structural lipids located in cortex and cuticle membranes and in the medulla, contributing ~2–6% of the overall fi ber weight. Sebum lipids can also contribute to fi ber health (1) but this is outside the scope of this work. The internal lipids in hair are mainly composed of fatty acids, cholesterols, and ceramides with fatty acids being the major components. An excellent review from Clarence Robbins in 2009 (2) details the proposed location of these lipids in the cell membrane complex (CMC). The bound lipids, including 18-methyleiconsanoic acid, are located in the cuticle CMC along with both free unsaturated and saturated fatty acids predominantly of chain length C16 and C18 in a monolayer arrangement. Cholesterols and ceramides are located primarily in the cortex CMC in a bilayer arrangement along with additional free fatty acids. The literature data are somewhat inconsistent on levels of these different lipids because of substrate variability and extraction techniques but it agreed that the lipids are important to hair health playing a major role in adhesion of cortical and cuticle cells. This makes them an important factor for determining hair strength and as a pathway for active penetration. It is also well known that daily weathering can cause loss of these internal lipids. Masukawa et al. (3) quantifi ed this loss after repeated shampoo treatments with and without bleaching and our work was to investigate mechanisms. This work describes a multistage extraction process to quantify the lipids and used to this method to investi- gate mechanisms by which lipids are changed during exposure to external stressors, such as bleaching and UV, and how this impacts hair strength. In addition, a strategy to replen- ish these lipids when lost is discussed. EXPERIMENTAL HAIR SAMPLES AND TREATMENT Four grams, 8-inch Caucasian-source untreated hair (i.e. no chemical treatment) was pur- chased from International Hair Importers & Products, Inc. (Glendale, NY). Each wash cycle consisted of applying 0.1 g/g shampoo to the hair tress and lathering for 30 s followed by a 30-s rinse repeated for a total of two shampoo applications. Hair tresses were placed in a hot box at 80°C until the hair was dry. The hair was then soaked in a solution of 6% hydrogen peroxide, 2% ammonium hydroxide adjusted to pH 10, with acetic acid for 35 min and then rinsed for 15 min to create chemically treated hair. INTERNAL LIPID AND FATTY ALCOHOL (FaOH) EXTRACTION Hair samples were equilibrated in a 20% relative humidity (RH) constant humidity chamber overnight. For each sample, ~0.1 g of hair was cut in 20–40 mm segments into vials (n = 4). First, the hair was extracted gently with hexane to remove the external surface lipid. The hexane extraction consists of extracting the hair with hexane two times then concentrating the dried residue in second solvent (mobile phase for the SFC- MS-MS and c derivatizing reagent for the GC). Next free lipid was extracted using 2:1 then 1:1 chloroform:methanol. The chloroform contained 10 mM dimethylhexylamine and the methanol contained 1% formic acid. Each extraction was heated for 30 min