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.

PREPRINTS OF THE 1996 ANNUAL SCIENTIFIC MEETING 255 Figure 3. Effect of chronological and growth aging on moisture retention. Figure 4. Effect of in vitro lipid treatment on extensibility. Figure 5a. Effect of in vivo lipid treatment on tensile strength. / I--IAfter Figure 5b. Effect of in vivo lipid treatment on moisture retention. Figure 5c. Effect of in vivo lipid treatment on extensibility.