I. Soc. Cosmet. Chem., 27, 579-592 (December 1976). Observations on the Cutting of Beard Hair DONALD E. DEEM, M. S. and MARTIN M. RIEGER, Ph.D.* Synopsis: A device is described which permits measurement of the force required to CUT a BEARD HAIR FIBER under a variety of conditions. Studies with this device show that the force required to cut wet beard fibers with commercial razor blades is about 65 per cent less than that of dry fibers. Beard hair is almost completely hydrated by exposure to water for about 2 minutes at room teanperature, and this hydration is accelerated by an increase in temperature. The force required to cut a beard hair increases with increasing fiber cross-sectional area, but this correlation is not perfect. The force required to cut beard hair is not lowered below that in water by the presence of a wetting agent, a shaving cream, or a soap solution. The force required to cut wet beard hair with a razor blade is lowered significantly by very severe attack on the fiber. On the other hand, the force required to cut beard hair increases as the rate of blade travel increases. •NTRODUGTION Since the classical study by Hollander and Casselman (1) very few publi- cations have dealt with the physics of shaving or the cutting of beard hair. Their study was based mainly on subjective evaluations by shaving panelists and included only minimal objective information obtained by mechanical testing (creep measurements ) and microscopic examination. The present study was designed to measure the force required to cut single beard fibers with commercial razor blades under conditions approximating the in vivo situation. No attempt was made to analyze the problem of hair cutting mathemati- cally. In accordance with the classical concepts of Duprd (2) one approach might be to equate the work-to-cut to the work to create two new cross-sec- tional hair surfaces plus frictional effects. Another approach would utilize a mathematical treatment of the elasticity of anisotropic materials, which ac- cording to Muskhelishoili (3) is extremely complex. *Personal Products Division, Warner-Lambert Company, 170 Tabor Road, Morris Plains, N.J. 07950. 579

580 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (a) ,.,','- ,,,_-.----":.• •-T• F-tE-.' '•""' Rubber Tubing (b) Section A 3/4" 0.010" ID Syringe --Tubing Figure 1. Beard Cutting Jig: (a) Overall view (b) construction details. Jig is constructed of brass and supported with brass rod and base. Rollers are % in. i.d. rubber tubing xvith 1/16 in. walls. Syringe tubing is set into hole flush with front face