PREPRINTS OF THE 1996 ANNUAL SCIENTIFIC MEETING 255 Aging hair in vivo and in vitro: The effects of cosmetic ingredients DAVID E. CINCOTTA and BARRY KARPF, Natural & Marine Resources, Inc,, Paramus, New Jersey, INTRODUCTION The hair cuticle is important in maintaining a resistant barrier against the environment, controlling to a degree the transport of water into and out of the hair shaft. It is also important in maintaining the optimal cosmetic attributes of hair and protecting the cortex from structural damage. The cuticle is held together by lipids forming intercel- lular membranes between cuticle cells just as in the stratum corneum. METHODS Treatments containing ceramides, free fatty acids, triglycerides, and esters, mimicking the structure of skin and hair membrane lipids, were applied to the various hair samples, and properties were evaluated. An extract of North American wheat sphingolipids and oils expressed from Asian green olives was added to a simple shampoo (0.5%) and a simple conditioner (1%) and tested in vitro and in vivo. Individual hair strands were obtained for in vitro experiments and segregated into two groups with average ages of 22.6 and 58.0 years, respectively. To simulate UV aging in certain experiments, hair was irradiated with a combination UVA/UVB light source from Kratos. Hairs were soaked for five minutes in shampoo (25% dilution), rinsed thoroughly with water, soaked for five minutes in conditioner (25% dilution), rinsed thoroughly with water, and air-dried to simulate a typical hair cleansing cycle. This cycle was repeated ten times, and the hair strands were allowed to equilibrate at 40% RH for 24 hours prior to testing. Tests were performed in the root section (0-10 cm from the root) and distal section (20-30 cm from the root). In vivo experiments were conducted by instructing the test subjects to wash their hair (five times per week) and apply conditioner (at least three times per week) during a four-week period. Hair samples were taken from each subject prior to and after the test period. All hair strands were equilibrated at 40% RH for 24 hours prior to testing. Tests were performed in the root section (0-10 cm from the root). Tensile strength was measured with a mini-Instron. Segments were 10 cm in length, attached at both ends, and elongated at the rate of 2 cm/minute. Elongation was measured with the Gas Bearing Electrodynamometer (GBE) with low force elongation and relaxation cycles. Hair water content was also measured with the GBE. Strands were soaked in water after various treatments, and the change in hair elasticity was used as an indirect measure of water content to determine the length of time hair strands would hold on to externally added water.

254 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS • L•E•p. Figure 1. Effect of chronological and growth aging on tensile strength. RESULTS Tensile strength decreases during chronological aging, as the older group showed a 9.0% loss in tensile strength (to break) at the root compared to the younger group (Figure 1). Growth aging on the scalp (evaluating root segments of hair and hair from the distal end) showed a greater effect as tensile strength decreased 9.5-12.1%. Hair artificially aged with UV exposure showed a greater loss whether from younger or older subjects, with losses of 13.3% and 14.8%, respectively. Distal tensile strength loss between younger and older subjects was only 6.3%, suggesting that environmental effects during growth aging play a greater role than chronological aging. Similarly, low stress hair extensibility at the root section decreased 8.2% between younger and older groups, but growth aging revealed large and significant changes in extensibility: over 15% in both groups (Figure 2). The ability to retain moisture at lower humidity was strongly affected by growth aging: moisture retention decreased among the younger and older groups by 22.7% and 27.9%, respectively (Figure 3). There was no significant difference in moisture retention due to chronological aging alone. UV exposure paralleled growth aging, with a 27.6% loss of moisture retention. In vitro lipid treatment greatly increased the moisture retention ability of distal hair by 25.5 to 29.0% (appr6ximately 10% improvements were observed in root hair, but these were not statistically significant). Similar improvements in moisture retention were observed with UV-damaged root hair (Figure 4). Finally, in vivo lipid treatment produced significant improvements in tensile strength (10.5%), extensibility (8.4%), and moisture retention (! !. !%), as seen in Figures 5a, 5b, and 5c. CONCLUSION Hair aging can be considered to result from chronological aging of the test subject, 4 Figure 2. Effect on chronological and growth aging on extensibility.