J. Cosmet. Sci., 62, 383–391 ( July/August 2011) 383 The uptake of water hardness metals by human hair A. O. EVANS, J. M. MARSH, and R. R. WICKETT, James L. Winkle College of Pharmacy, University of Cincinnati, 3225 Eden Avenue, Cincinnati, OH 45267-0004 (A.O.E., R.R.W.), and The Procter & Gamble Company, Miami Valley Innovation Center, 11810 East Miami River Road, Cincinnati, OH 45252 ( J.M.M.). Accepted for publication April 19, 2011. Synopsis The objective of this work was to examine the variables that infl uence the interaction between water hardness metals and human hair. Hair extracts various constituents from the tap water used during daily hygiene practices and chemical treatments. Calcium and magnesium metal ions are the most prevalent and give water “hardness.” Inductively coupled plasma atomic emission spectroscopy (ICP-AES) was employed to quantify the metal content of hair, which was studied as a function of the following variables: hair condition (oxidative damage), level of water hardness, and water pH. We have demonstrated that these variables impact water hardness metal uptake to varying extents, and the effects are driven primarily by the binding capacity (available anionic sites) of the hair. The condition of the hair, a key representation of the binding capacity, was most infl uential. Interestingly, water hardness levels had only a small effect on uptake hair became saturated with notable amounts of water hardness metals even after repeated exposure to soft water. Water pH infl u- enced metal uptake since side chains of hair proteins deprotonate with increasing alkalinity. These insights highlight the importance to the hair care industry of understanding the interaction between water hardness metals and hair. INTRODUCTION The uptake of metal cations, specifi cally redox active metals, by various types of keratin fi bers has been investigated in the scientifi c literature (1– 4). However, less attention has been focused on water hardness metals, particularly from a consumer-relevant standpoint. Calcium and magnesium metal ions are most prevalent in tap water and give water “hard- ness.” Acting as an cation-exchange resin, human hair has been reported to extract up to 10,000 ppm of these metal ions from the tap water used during hygiene practices (5), and consumers associate the use of hard (and soft) water with differences in various structural and cosmetic properties of hair. Given that human hair is exposed to water for a signifi - cant portion of its lifetime, an understanding of the interaction between the components of water and hair is important. Past research efforts have established the location of water hardness metals in hair. This work has indicated that calcium is present primarily in the cuticle of hair fi bers. Kempson et al. and Mérigoux et al. used the imaging capabilities of time of fl ight secondary ion

JOURNAL OF COSMETIC SCIENCE 384 mass spectrometry (ToF-SIMS) (6) and scanning X-ray fl uorescence microscopy (SXRF) (7), respectively, to study calcium in hair. Mérigoux et al. found calcium in the cuticle layers and granules in the cortex and within the medulla. Kempson et al. showed calcium accumulations at the cuticle edges where carboxyl groups are likely available from the exposed endocuticle, as well as the aforementioned internal structures of this chemical nature. There is also evidence that calcium and magnesium may be present as salts of lipid material (8,9). Using nanoscale secondary ion mass spectrometry (Nano-SIMS), Smart et al. (10) confi rmed calcium accumulation in the A-layer and exocuticle of bleached hair, areas containing large amounts of sulfur. Although the uptake of redox metals by human hair has been documented as a function of solution metal concentration, solution pH, and chemical treatment of hair (11,12), only a few studies have examined the uptake of water hardness metals under these condi- tions. Uzu et al. (13) studied calcium uptake by cold-wave permed hair, and observed a positive correlation between uptake, solution pH, and hair treatment. Noble (14) exam- ined the uptake of calcium and magnesium from tap and processed (bottled) water sources from various geographic locations. By measuring the change in the pH and the total hardness of the test waters before and after vortexing the hair in the water, he concluded that both parameters infl uenced the uptake of hardness metals by hair. As the hair sam- ples were collected from men, women, and children, there was no consideration for the condition of the hair or any parameters that would differ with habits and practices, age, and/or sex. The highlighted research efforts clearly provide a lead on understanding aspects of the interaction between water hardness metals and hair, but they also indicate the need for well-controlled, consumer-relevant work. We have addressed this opportunity area by systematically studying the uptake of calcium and magnesium as a function of the follow- ing key variables: hair condition, water hardness level, and water pH. We hypothesized that these variables infl uenced the uptake of water hardness metals by hair because they were related to the binding capacity and amount of metal ions available for interaction. MATERIALS AND METHODS HAIR SAMPLE PREPARATION AND CHARACTERIZATION Virgin, dark brown Caucasian hair swatches were the starting substrate for this work (1.5 g/16 cm International Hair Importers and Products, Glendale, NY). Slightly damaged and highly damaged hair substrates were prepared by treating this hair with a 12% active hydrogen peroxide oxidant crème for one cycle of 15 minutes and three cycles of one hour, respectively. The oxidant crème contained 5% Crodafos® CES (a mix of cetearyl alcohol, dicetylphosphate, and ceteth-10 phosphate Croda) and 1.2% ammonium hydroxide. The oxidative bleaching treatment was carried out in a 30°C oven to simulate scalp tempera- ture. Immediately following bleaching, the hair swatches were rinsed with deionized wa- ter (Milli-Q) for one minute, fan-dried, and equilibrated at room temperature for at least 24 hours before any further treatment. This was considered baseline for the swatches. The condition of the virgin and bleached hair substrates was characterized by measur- ing surface cysteic acid content using a previously detailed Fourier transform infrared