J. Cosmet. Sci., 62, 191–202 (March/April 2011) 191 Spectrofl uorescent characterization of changes in hair chemistry induced by environmental stresses ROGER L. McMULLEN, SUSAN CHEN, and DAVID J. MOORE, Materials Science Dept., Corporate R&D, International Specialty Products, Wayne, NJ. Synopsis Hair is frequently exposed to environmental stresses and chemical insults that result in damage to its internal structure and its outer cuticular components. Spectrofl uorescence is a useful tool to monitor the health of biological tissues as it can measure the level of tryptophan (Trp), which is representative of protein integrity. In addition to Trp fl uorescence, several other fl uorophores are also present in hair and are believed to be at- tributed to kynurenenine, N-formylkynurenine, and 3-hydroxykynurenine, which are known metabolic and degradation products of Trp that are affected by environmental stresses normally experienced by hair. In this work, we were able to construct an endogenous fi ngerprint of fl uorescent compounds present in hair by em- ploying a range of excitation wavelengths from 270 nm to 450 nm with a resolution of 2 nm. As a result, we generated surface plots of fl uorescence emission as a function of excitation and emission wavelengths (excita- tion-emission matrices). Thus, we were able to profi le the levels of various structural molecules in hair before and after exposure to UV irradiation and thermal straightening irons as well as to chemical treatment such as bleaching and straightening. INTRODUCTION Human hair is constantly exposed to environmental insults that damage the fi ber and reduce its biological integrity. In addition to natural stresses, such as UV irradiation, hair is often subjected to other chemical and physical treatments. For example, hair may be damaged by mechanical grooming procedures or thermal treatments carried out with hot irons. Chemicals treatments, such as permanent waving, hair straightening with relaxers, and bleaching of hair, are also very damaging to hair. Typically, permanent waving is ac- complished by treating the hair fi rst with a reducing agent (e.g., mercaptoethanol) to break disulfi de bonds, then once hair is manipulated in the desired formation, it is treated with H2O2 in order to reform the disulfi de links (1). Historically, hair straightening was achieved with lye relaxers (containing NaOH), which are very damaging to hair’s mor- phological and chemical structure (2). More recently, slightly less basic reagents have been introduced as straightening agents however, lye relaxers are still commonly em- ployed. Hair bleaching, nowadays still a very common procedure, employs H2O2 used in conjunction with accelators (salts of persulfates), which results in hair surface damage and destruction of internal components of hair, including melanin and proteins (3,4). The subject of photodegradation of hair has recently received a great deal of attention in the

JOURNAL OF COSMETIC SCIENCE 192 literature (5,6), while thermal degradation has been studied signifi cantly less (7-9). Nev- ertheless, exposure of hair to either one of these insults results in internal protein damage (cortical) as well as detrimental effects to the outer cuticular components. There are many biochemical techniques available, which allow for specifi c protein deter- minations, thereby permitting one to monitor the quantity of protein present in hair so that comparisons can be made among population samples. Unfortunately, these tech- niques require the destruction of the hair fi ber and subsequent, time-consuming proce- dures and analyses. Measuring the fl uorescence of biological tissues with an external fi ber optic probe is frequently utilized due to its non-invasive nature and ease of use. Typically, Trp is monitored due to its intrinsic fl uorescence and because it serves as an indicator of overall protein damage. Such studies were carried out to monitor Trp fl uorescence and to investigate the presence of other fl uorophores in hair (7,10–12). In the current study, we monitor the damaging effects of environmental and chemical insults to hair by employ- ing steady-state fl uorescence to generate excitation-emission matrices. The matrices pro- vide full fl uorophore characterization of the biological substrate under investigation. EXPERIMENTAL MATERIALS In order to observe differences in hair damage resulting from hair pigmentation, studies were carried out with European dark brown (International Hair Importers & Products, Glendale, NY) and Piedmont hair (DeMeo Brothers, Passaic, NJ). Hair tresses were pre- pared by gluing 2 g of fi bers to a 1.5-in. × 1.5-in. plexiglass tab with Duco Cement. The resulting dimensions of all hair tresses were 6.5 inches in length and 1.25 inches in width. Hair tresses were precleaned with a 3% ammonium lauryl sulfate solution and rinsed thoroughly prior to use in the experiments. Hair relaxer treatments were carried out using Revlon Realistic Creme Relaxer (Colamer U.S.A., Inc., Dist. New York, NY), which contains: water, petrolatum, parrafi num liq- uidum, cetearyl alcohol, propylene glycol, sodium hydroxide, polysorbate 60, cetyl alco- hol, leneth-15, PEG-60 lanolin, potassium cocoyl hydrolyzed collagen, PEG-150 stearate, steareth-20, and fragrance. Hair was bleached using Clairol Professional BW 2 (Clairol, Stamford, CT) bleaching powder containing potassium persulfate, ammonium persulfate, sodium metasilicate, so- dium stearate, silica, hydrated silica, hydroxypropyl methylcellulose, aluminum distear- ate, sodium lauryl sulfate, disodium EDTA, and sorbitol. The bleaching powder (120 g) was mixed with 147 mL of Clairoxide 20 volume (Clairol, Stamford, CT) developer ac- cording to the manufacturers instructions. The developer contained water, H2O2, and phosphoric acid. INSTRUMENTATION Fluorescence measurements were carried out on a steady-state spectrofl uorometer (FluoroMax-4) manufactured by Horiba Jobin Yvon (Edison, NJ) equipped with a bifur- cated fi ber optic probe. The fast and accurate scanning capability of the instrument (80 nm/s)