J. Cosmet. Sci., 64, 111–117 (March/April 2013) 111 Cytokine expression correlates with differential sensory perception between lye and no-lye relaxers ROBERT N. TACKEY, HAROLD BRYANT, and FELICIA M. PARKS, L’Oreal Institute for Ethnic Hair and Skin Research, Chicago, IL 20616. Accepted for publication July 23, 2012 Synopsis Differences in perceived sensory scalp discomfort between guanidine carbonate/calcium hydroxide (no-lye) and sodium hydroxide (lye) relaxer technologies have been reported by users for decades. However, the bio- chemical processes responsible for the perceived differences have not been fully studied. We have used an in vitro three-dimensional skin model with well-developed epidermis to explore the expression of cytokines that may partially explain the biological response resulting in differences in sensory perception. The cytokines selected were prostaglandin E2 (PGE2), interleukin-1α (IL-1α), and IL-1 receptor antagonist (IL-1ra) because they have been shown to participate in irritant-induced discomfort. We show that lye relaxer induced over 350% increase in PGE2 expression over untreated control compared to 200% by no-lye in the early phase (4 h) postexposure epidermal response. Expression of IL-1α in the early phase showed no signifi cant difference between lye and no-lye however, no-lye induced higher levels (p 0.0001) in 24 and 48 h. Concomitantly, no-lye induced increased expression of IL-1ra compared to lye at all time points. Given the association of PGE2 with nociceptive activation, these fi ndings suggest that the perceived variation in sensory discomfort reported by consumers between lye and no-lye relaxers may be associated with differ- ences in induced PGE2 expression. INTRODUCTION Hair relaxers are complex cosmetic formulations consisting of many ingredients and are designed to permanently straighten curly hair. The active ingredient in these emulsions is the hydroxide ion, which can be quantifi ed by measuring the pH of the formulation. Lye and no-lye are the two main types of relaxers used in the United States to straighten curly hair. Lye relaxers contain sodium hydroxide as the source of hydroxide ion. No-lye relaxers contain calcium hydroxide and guanidine carbonate, which when combined pro- vides the source of hydroxide ions. Hair relaxers are not designed to be in direct contact with the scalp, but through the process of use, contact may occur. Although measures including, but not limited to, the application of petrolatum (basing) to the scalp are Address all correspondence to Robert N. Tackey at RTackey@rd.us.loreal.com

JOURNAL OF COSMETIC SCIENCE 112 practiced to limit contact with the scalp, complaints of discomfort still arise (1,2). It is common for cosmetic products to induce discomfort including itching, stinging, and burning sensations if used incorrectly (1). Although some of these complaints are associ- ated with overuse or misuse, there remains a difference in consumer-perceived discomfort potential between the two most widely used relaxers in the United States. A population-based in vivo study showed that majority of relaxer users perceive no-lye relaxer as less irritating than lye relaxer regardless of whether the discomfort is rated as severe, moderate, or mild (2). Results reported were based on comfort/discomfort evalua- tions of over a thousand salon patrons as an indication of irritation potentials of the two types of relaxers. While reported, these differences are not linked to formulations or bio- chemical processes through scientifi c experimentation. However, there are good reasons to believe that cytokines may be involved as several studies provide evidence of the role of cytokines in inducing sensory discomfort and infl ammation (3–5). Acute infl ammatory pain is characterized by hypernociception due to sensitization of primary sensory neurons. Furthermore, it has been shown that specifi c primary cytokines are released after tissue injury to act on membrane sensory receptors to trigger sensory activation. The nature and type of mediators released depend on the nature of tissue injury. Chen et al. (6) have dem- onstrated the mechanical sensitization of cutaneous C-fi ber nociceptors by prostaglandin E2 (PGE2) in the rat, which provides the basis for studying its possible role in relaxer- induced discomfort. However, no comparative profi ling of cytokines responsible for these perceived differences between lye and no-lye relaxers has been done to date. In this investigation, we used a well-developed three-dimensional reconstructed human epidermis (EpiSkin™ Figure 1) to examine the types and quantity of cytokines associated with sensory irritation that may provide a partial explanation for the perceived differences in discomfort between lye and no-lye relaxers. The cytokines selected in this study are those suggested and confi rmed by many authors (7–9) as being good predictive indicators in both short- and long-term exposure response by the epidermis. MATERIALS AND METHODS MATERIALS Two se parate lots of EpiSkin™ model (1.07 cm2) supplied as a 12-well kit and all neces- sary accessories were purchased from SkinEthic Laboratories (Lyon, France). Upon arrival, tissue inserts were removed from agar and placed in 12-well culture plate containing 2 ml of maintenance medium. Transferred tissues were incubated at 37oC, 5% CO2, and 95% relative humidity for a period of 24 h before using for all experiments. Consumer lye (Mizani, Chicago, IL) and no-lye (Optimum Care, New York, NY) relaxers were pur- chased and used according to instructions in the product insert. PRODUCT APPLICATION Separate EpiSkin™ tissues were topically exposed to75 μl each of medium strength lye relaxer or no-lye relaxer for exactly 15 min. Treated tissues were washed three times, each