Chapter 14 453 in their effectiveness during the hair growth cycle. Furthermore, β-endorphin was shown in this study5 to play a role in the regulation of human hair pigmentation. Data from two large studies on graying: Hair graying is closely related to chronological age, and within the bounds of today’s technology, the age of its onset is largely controlled by genetics. A review of the hair graying process by Tobin and Paus2 states that the average age of onset of gray hair for Caucasians is in the mid-30s, while for Asians it is in the late 30s and for those of African descent it occurs in the mid-40s. One large study involving the incidence of graying was conducted by Keogh and Walsh in 1965 in Australia.6 This study included subjects 25–60+ years of age. Because Keogh and Walsh found no significant difference in the graying of hair of males versus females, they combined the male and female data and separated it into 5-year age increments. This study contained a total of 8,720 persons, including 6,653 men and 2,067 women. This paper did not specify racial characteristics of the group however, since the data is from Victoria, Australia, it may be assumed that the data largely or totally represents Caucasians. The study included persons who had dyed their hair and those who had not dyed it. The authors stated that when the hair had been dyed or suspected of being dyed, they relied on the subject’s own statement regarding the true color and degree of grayness prior to dyeing. The authors indicated further that preliminary trials showed the subjects to be in substantial agreement with ratings by trained observers. For those subjects who had not dyed their hair, these scientists first experimented with standards of cut hair, then with photographs, and finally chose to rely on the trained observers’ judgments regarding only two categories of graying: any gray, and complete or total gray. The effect of hair color on the perception of graying: The afore- described study6 did not provide any significant difference in either percentage (%) of “any gray” or % “complete gray” of males versus females. However, significant differences were found in the ability to see graying as a function of the three hair color types described in Table 1.