J. Cosmet. Sci., 67, 93–100 (March/April 2016) 93 Use of optical profi lometry and visual grading for measurement of longitudinal striations of the nail CELIA LUDWINSKI, AXELLE CLOCHARD-BOSSUET, THERESA CHEN, KELSEY NORWOOD, and CHRISTIAN ORESAJO, L’Oréal USA Research and Innovation, Clark, NJ 07066. Accepted for publication April 10, 2016. Synopsis Consumer perception of longitudinal striations of the nail is one of the drivers of nail cosmetic purchase and use. The following work investigates the use of objective instrumental methods for the characterization of longitudinal striations. Striations are quantifi ed by Ra (the average maximum height of the profi le), Rq (the root mean square average of the roughness profi le), and Rz (the mean roughness depth), industrial roughness parameters, which are calculated using optical profi lometry of the three-dimensional surface structure of the nail. A visual assessment is conducted by cosmetologists in vivo and on images captured in several lighting conditions. With this evaluation, the cosmetologists provide ratings of surface ridges on a 0–5 scale to com- plement and validate the instrumental method. Both the optical profi lometry and the cosmetologist-graded methods are used to evaluate 33 nails of visually-varying levels of ridges from female volunteers. The evalu- ations from these methods yield well-correlated and repeatable results, and these preliminary fi ndings sug- gest that this new instrumental method can be used to objectively measure longitudinal striations of the nail. INTRODUCTION Consumer perception of cosmetic imperfections of the nail is one of the drivers of nail enamel use. Yellowing, spots, chipping, peeling, thinning, brittleness, and striations are examples of imperfections that can be concealed with cosmetic products. In particular, the appearance of longitudinal striations is a major motivation for the purchase of correc- tive or concealing cosmetic enamels. In light of this trend, this article focuses on the de- velopment of an objective method for the characterization of longitudinal striations. Longitudinal striations can be categorized into two physiological presentations: surface and underface ridging. Surface ridging is what the naive consumer typically refers to as nail ridges and is included in the clinical classifi cation of onychorrhexis. Surface ridging presents as superfi cial parallel ridges and valleys of the nail plate surface, which extend from the proximal nail fold to the distal nail edge (1–5). Comparatively, underface ridging consists of parallel ridges from the proximal nail fold to the distal nail edge Address all correspondence to knorwood@rd.us.loreal.com.

JOURNAL OF COSMETIC SCIENCE 94 without affecting the outer surface of the nail (5). The methodologies developed in this article focus on surface ridging as it is the consumer’s primary cause of concern. To the consumer, longitudinal striations deviate from the healthy nail ideal because of the dull, rough effect imparted on the nail surface appearance and feel. In fact, the healthy nail plate is typically associated with a well-groomed appearance and a smooth, lustrous surface (2,3,5–7), whereas striations signal unhealthy and aged nails (6). To address these concerns, the consumer treats longitudinal striations through diet, cosmetic techniques such as buffi ng, and the use of cosmetic products such as ridge fi llers and enamels. The study of longitudinal striations is thus interesting from multiple perspectives: in terms of its signifi cance for consumers’ motivations for product usage and from a knowl- edge standpoint, because of the known association between striations and aging (2). Still, the subject of striations suffers from a dearth in objective methodologies, as an over- whelming majority of the related work presented in literature has been conducted clini- cally. Usually in such cases, nails are broadly described, and a scale will not be explicitly defi ned. These clinical descriptions of longitudinal striations are also frequently accom- panied by digital photography to be used as reference and to track a nail’s changes over time, though most do not use consistent image capture conditions. There is thus a need to develop an objective method for the consistent evaluation of lon- gitudinal striations. A methodology for measuring longitudinal striations is presented in this work. This proposed methodology relies on fringe projection as the method of optical profi lometry used to map the three-dimensional (3D) surface structure of the nail and on an industrial roughness parameter to quantify the superfi cial ridges at select cross- sections of the nail. To complement and validate this method, an additional methodology for classifying the overall severity of longitudinal striations was developed. This methodology—similar to clinical grading approaches—relies on a visual assessment conducted by cosmetologists on a 0–5 scale. The cosmetologist assessment includes the evaluation of the severity, num- ber, and depth of the longitudinal striations on the surface of the nail. The cosmetologist mindset offers an objective viewer with a familiarity for various nail conditions, but with a more naive, consumer-relevant perception of the nail than a trained dermatologist. Ultimately, an investigation into the repeatability of the instrumental method as well as a correlation between the two methods is presented. MATERIALS AND METHODS Thirty-three nails were selected to adequately represent fi ngernails from all 10 fi ngers, various ethnicities, a wide age range, and a representation of the range of longitudinal striations. The nails were measured in vivo using a fringe projection method and images were evaluated using the cosmetologist scale outlined below. The in vivo nail sample set was provided by 28 female volunteers who were between 18 and 70 years of age (average 45.6, with a self-declared ethnicity of African-American/ black (n = 8), east/southeast Asian (n = 7), Caucasian/white (n = 9), or Hispanic/Latina (n = 4). All subjects were recruited from an internal database and gave informed consent for this research to be performed. Data collection was done from March to June 2013. All subjects had self-perceived healthy nails, although brittle, peeling, and fl aking nails were