SCALP HAIR LENGTH 373 i -10- - -15.. -20 0 J i I 125 250 375 500 Hair Length in Centimeters Figure 3. Plot of the natural logarithm of the percentage of the population versus hair length up to currently documented hair lengths (in centimeters). about Lu Seng La, touted by Ripley's as possessor of the world's longest hair, and an internet article from the Godrej Hair Care Institute (9) about Diane Witt. The focus of the tabulated data are primarily from the past ten years rather than older data, which were purposely excluded. These longer hair lengths from the literature (183 cm [six feet] and longer) come from people from all over the world. Therefore, percentages were calculated based on the number of people at that hair length relative to the world's population of 6 billion people, assuming 4.5 billion as adults, since 75% of the world's population are age 12 and above (10) (see Table VI). As our discussion and data below show, there undoubtedly are more people in the world with hair length between t83 cm and 518 cm (between

374 JOURNAL OF COSMETIC SCIENCE Figure 4. The long hair of Crystal Gayle. Hair to the ankles can be observed in only a small percentage of the population. (Published with permission of Gayle Enterprises, Inc.) six and 17 feet) than listed in these websites, but we believe that our discussion below shows that our primary conclusions will not change appreciably even if there are more persons with hair between these lengths. Figure 3 is a plot made by combining the data on hair length from our USA theme park studies with the data of Table VII. In this graph, we assume that the USA data (percentages) represent data for the whole world. For the developed world this assump- tion probably holds reasonably well. However, for developing-world countries like India, China, and Indonesia, with a higher percentage of very young people (Table II) and where there is less cutting of hair, especially among females, this assumption will likely provide low estimates. Obviously, this assumption provides greater deviation at shorter hair lengths because of the limits imposed by common anagen growth periods, usually cited at two to six years