J. Cosmet. Sci., 63, 27–31 (January/February 2012) 27 Quantitative measurement of the penetration of coconut oil into human hair using radiolabeled coconut oil V. GODE, N. BHALLA, V. SHIRHATTI, S. MHASKAR, and Y. KAMATH, Marico Research Centre, Marico Ltd., Mumbai, India (V.G., N.B., V.S., S.M.), and Kamath Consulting Inc., 11 Deer Park Drive, Monmouth Junction, NJ 08852 (Y.K.). Accepted for publication June 9, 2011. INTRODUCTION Applying oil to hair and skin is an age-old tradition in Asian and African countries. The traditional system of medicine in India, Ayurveda, has several formulations of oils (based mainly on coconut and sesame) with herbal extracts. These oils are supposed to benefi t both hair and the hair follicle. Generally, these oils are applied as prewash hair dressings. This is also true of plain oils without any herbal actives. In either case, the hydrophobicity of the oil plays an important role in protecting hair from damage. Surface lubrication is the fi rst level of defense against abrasive damage in grooming. A more signifi cant factor is the protec- tion of hair and especially the hair follicle from surfactant damage. Low-molecular-weight surfactants such as sodium lauryl sulfate (SLS) in shampoos can penetrate easily into the structure of hair and interfere with the formation of secondary valence bonds such as hydro- gen bonds and salt linkages. This can weaken hair. On the positive side, penetrated oil can reduce the amount of water absorbed in the hair, leading to a lowering of swelling. This can result in lower hygral fatigue (repeated swelling and deswelling), a factor which can damage hair. The softening effect of moisture is replaced by the plasticizing effect of oil. As far as the follicle is concerned, the oil can fi ll the gap between the hair and the follicle wall and prevent the penetration of the surfactant solution into the follicle. Surfactant molecules like SLS, when penetrated into the follicle, can interfere with the adhesion of follicular structures, leading to loosening of hair in the follicular cavity, ultimately leading to hair loss. Applying oil on a regular basis can eliminate follicular damage leading to hair loss. The overall effect is a head full of rich and long hair. The fi rst attempt to show the penetration of hair by coconut oil (CNO) was made by Ruetsch, Kamath, et al. (1). The method used was time-of-fl ight secondary ion mass spec- trometry (TOF-SIMS), which was able to map the molecules of CNO in the cross section of hair treated with CNO. Although the method could show the depth of penetration, it was incapable of yielding quantitative (how much) data. Since then, the TOF-SIMS method has been used by Hornby et al. (2) to study the penetration of other vegetable oils.
JOURNAL OF COSMETIC SCIENCE 28 However, the TOF-SIMS method, by its very nature, is qualitative. It cannot be used to determine the amount of oil that has penetrated into the hair. Therefore, the present work is aimed at developing a method that can provide quantitative data on the penetration of CNO into human hair, using radiolabeled CNO. EXPERIMENTAL MATERIALS CNO was provided by Marico Limited, Mumbai, India. Solvents, such as alcohol, dioxane, and toluene, were of AR grade and were obtained locally. This work was done at Bhabha Atomic Research Centre (BARC) in Mumbai, India. PREPARATION OF RADIOLABELED (3H SUBSTITUTED (TRITIATED)) CNO A known amount of CNO was dissolved in dioxane, and the solution was heated in the presence of tritium gas at 120°C for two hours in the presence of a catalyst (of proprietary composition). Following tritiation, the solvent was evaporated on a Rotovap, and the tritiated CNO (TCNO) was brought to a fi nal volume of 1.5 ml with unlabeled oil. This oil mixture was used in all the studies presented in this communication. HAIR TREATMENT A 10-cm-long strand of Indian hair weighing 100 mg was soaked in 1.5 ml of TCNO. Hair specimens were taken from this sample after one and six hours for further analysis. Surface oil was determined with two single hair fi bers, and penetrated oil was determined on fi ve single hair fi bers taken from the 100-mg sample. Measurements for each treatment time (one and six hours) were made in triplicate sets. The hair specimens were gently blotted on tissue paper soon after their removal from the oil-soaked strand in order to remove the extraneous oil. The approximate weights of two and fi ve hair fi bers were 1.22 mg and 6.1 mg, respectively. RADIOACTIVITY MEASUREMENTS A unique property of tritium is that it is a beta emitter, and therefore, to register its emission it has to be in direct contact with the scintillation fl uid. This means that the TCNO inside the hair is not registered. This enables the measurement of substantive surface oil separately. In a typical measurement two hair fi bers were immersed in 10 ml of the scintillation fl uid and placed into the counter (Hidex, effi ciency 32%). The counts per minute (CPM) were recorded. For the determination of total oil in the hair (surface oil plus penetrated oil), fi ve hair fi bers were solubilized in 400 μ1 of 10% NaOH at approximately 70°C for one hour or until the solubilization of the sample was complete. Five microliters of the hydrolyzed hair solution was added to 10 ml of the scintillation fl uid, and the CPM was recorded after the solution was placed in the scintillation counter (Hidex).
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