54 JOURNAL OF COSMETIC SCIENCE EXPERIMENTAL To obtain data on the percentage of persons in the US with different lengths of scalp hair, we went to four theme parks in central Florida at different dates: to Epcot three times, on January 24, March 14, and March 21 to Universal Studios on February 6 to Magic Kingdom three times, on February 9, February 28, and March 28 and to MGM Studios on February 20. Our objective was to observe and count persons with different lengths of hair. We returned two additional times in April and May to obtain the data on hairstyles and headcovers. We believe that the population at these theme parks represents a good random assort- ment of normally active adults (of all ages) across the United States. We stationed ourselves at a few different sites in these parks (generally just inside the entrance and at one or two other busy spots inside the park) and counted the total number of persons (males and females) passing by who appeared to be large young persons or adults, generally estimated to be 12 to 14 years of age or older and generally about 137 centimeters (41/2 feet) tall or taller. We observed and counted a total of 24,300 persons--- 3,000 at Epcot each time 3,000 at Universal 3,300 at Magic Kingdom on February 9 and 3,000 on February 28 and on March 28 and 3,000 at MGM Studios. The study on hairstyles was conducted on March 21 at Magic Kingdom to try to determine whether or not any hairstyles might interfere with or affect our estimates on free-hanging hair length. For this study, we classified passersby as having one of three types of hairstyles: free-hanging hair styles ponytails or braids and buns or styles bound to the scalp that might interfere with an estimate of free-hanging length. We also tried to estimate from the size of the hair bound to the head whether it was shorter than waist-length or longer than that length. The study on headcovers was conducted on May 9 at Epcot, to try to determine whether or not any headcovers might interfere with our hair length estimates. In this study, we classified four groups: no headcover caps (primarily baseball-type caps including sun visors) hats and scarves/hoods. For the hats and scarves/hoods we also tried to estimate those that interfered with our estimate of free-hanging hair length and those that did not. DISCUSSION HAIR GROWTH AND FACTORS AFFECTING SCALP HAIR LENGTH Hair length is determined by our physiology, how we cut our hair, and hair breakage. The physiological factors affecting scalp hair length are: ß genetic-related, including age ß health-related, including medications that we take Genetic control of hair length. Normally our genes determine how long our hair can grow at different stages of maturity by controlling the release of hormones (primarily testos- terone) and other chemicals that affect hair growth. Hair growth is controlled in the living part of the fiber at the base of the hair bulb well beneath the skin surface. Each hair fiber grows inside a sac called a follicle. The cells at the base of the bulb divide and

HAIR LENGTH IN THE USA 55 move upward toward the skin surface and then eventually dehydrate and die as they form a part of the final fiber structure for which they were created (1). All human hair fibers have three distinct stages in their life cycle (1). The stage when the fiber is growing is called anagen. Telogen refers to the stage when the fiber stops growing and is resting, just before it is pushed out and replaced by a new growing hair in the same follicle. The intermediate stage between the growing stage and the resting stage is called catagen. The resting stage and the intermediate or transition stage each last about four weeks. The growing stage is highly variable in terms of how long it lasts, and its duration determines the length that each fiber can attain. Testosterone and other physiologic agents control the timespan of anagen (2). Scalp hair usually grows at the rate of about 13 centimeters (5 inches) per year (3,4), However, it does grow at slightly different rates on different parts of the scalp. Hair normally grows at a slightly lower rate on the temples compared to the crown area of the scalp. For most persons, scalp hair fibers that are never cut or broken off grow to somewhere between 60 to 122 centimeters (2 to 4 feet) in length (5). Much longer scalp hair has been observed in rare cases from an abnormal condition that interferes with the normal life cycle of hair. The G•inness Book of World Records since the 1960s has reported several persons with hair much longer than 4 feet. In fact, the longest reported and verified scalp hair for a man is that of Hu Sateow, a tribal medicine man of Chiang Mai, Thailand, with hair measured at 513 centimeters (16 feet 10 inches) by the Guinness group in 1999 (6), and the longest reported scalp hair for a woman is that of Mata Jagdamba of Ujjain, India, measured at 423 centimeters (13 feet 10.5 inches) in 1994 (7). Age and hair length. Since hormones and other physiologic agents are involved in deter- mining how long our hair can grow, it is not surprising that hair length varies with age. For example, infant hair usually does not exceed 6 to 8 inches in length (2), while the hair of children, prior to puberty, usually does not exceed 24 to 30 inches (2). Long hair may be seen in some women in their 40s and 50s and even older, but, with increasing age, the timespan of anagen usually decreases for both men and women (8). Data for the scalp hair diameter correlates with age and shows a maximum from the teenage years up into the 20s and then a decrease with increasing age (9). Since fiber diameter correlates with anagen timespans (3,8), and growth rates measured by length per unit of time correlate with anagen timespans (4), the fiber length (assuming no cutting of hair) must also show a maximum from the teenage years up into the 20s and then a decrease with increasing age. Consistent with this conclusion is the fact that in a 1972 hair length survey among 2,400 women, 44 percent of those in the 14 to 24 age group said that they had hair shoulder-length or longer while only 12 percent of those above age 35 had hair shoulder-length or longer (10) (see Table I). Even though the data of this survey is nearly 29 years old, a similar trend appears to exist today because in our current hair length studies, among the waist-length or longer group, the vast majority of those persons appeared to be in their 20s. We estimated only two of 77 persons in this very-long-hair group who appeared to be near 40 years of age or older. The numbers from the survey and our studies are influenced by hair-cutting tendencies as well as by anagen timespans. However, we believe that the anagen timespans are important to these numbers. Health, genetic disorders, medications, and hair length. Androgenic alopecia occurs in about