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J. Cosmet. Sci.J 56, 323-330 (September/October 2005) Penetration of cationic conditioning compounds into hair fibers: A TOF-SIMS approach S. B. RUETSCH and Y. K. KAMATH, TRI/Princeton, Princeton, NJ 08542. Accepted for publication June 8, 200 5. Synopsis Cationic conditioning compounds protect against hair damage caused by cosmetic chemical treatments and grooming practices. They also enhance the retention of moisture. However, the question as to whether they do this superficially by residing on the hair surface or by penetrating into the fiber remains unanswered. In this work, an attempt has been made to show the penetration of a low-molecular-weight cationic condi­ tioning compound into the hair cortex using the time-of-flight secondary ion mass spectrometry (TOP SIMS) method, applied in earlier research to show the penetration of oils into hair. An example of the practical benefit of such penetration into the cortex in greatly improving the fatigue resistance of hair has been discussed. INTRODUCTION Cationic conditioning compounds are often used to improve the cosmetic properties of hair, such as manageability, combability, and reduction of static charging, known as "flyaway." Most of the desirable effects are brought about by the small amounts of conditioner residues left on or in the hair fiber. Earlier studies have shown that these cationic conditioner residues reinforce the cuticle sheath of hair and reduce scale lifting, which occurs as a response of the surface cuticle cell when tensile stress is imposed on the hair fiber during grooming, especially when encountering a snag, or pulling and stretching the hair (1). Other properties of the hair assembly coveted by consumers and producers of hair care products are abrasion and fatigue resistance and retention of moisture. These attributes of conditioning compounds are often enhanced by the penetration of these compounds into the hair fiber. Although conventional concepts of diffusion doubt the penetration of high-molecular-weight polymer cationics (above a molecular weight of -1000) be­ yond the cuticular sheath, claims have been made to the contrary. We, therefore, pursued a study involving penetration of two cationic conditioning compounds, differing in chemistry and molecular weight, using a reliable method of identifying their residues within the hair fiber, especially at low concentration. Faucher and Goddard (2), using a radiotracer technique, showed the penetration of cationic cellulose-based polymers into the hair fiber. Similar studies were conducted 323