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

56 JOURNAL OF COSMETIC SCIENCE Table I Hair Length Survey: US Women--Hair Length and Age (Nov./Dec. 1972)(10) Hair length/Age groups 14 to 24 25 to 34 35 to 50 50 to 60 14 to 60 Short 11% 27% 34% 53% 33% Medium 45% 40% 52% 38% 43% Long 44% 33% 14% 10% 24% Number of panelists 512 518 664 706 2400 Short = chin-length or shorter. Medium = chin-to-shoulder length. Long = shoulder-length or longer. 40 percent of men and 10 percent of women (a bit higher after menopause) (11) and interferes with one's ability to grow long hair. Several congenital disorders weaken hair fibers, leading to greater than normal breakage, and thus limit the length that hair fibers can attain. Trichorrhexis nodosa, monilethrix, and pill torti are such ailments. Other disorders such as alopecia and telogen effluvium also interfere with hair growth and thus limit the length that hair can attain. A few medications such as streptomycin, cyclosporin, diazoxide, spironolactone and estrogens can lengthen anagen, thus producing longer and thicker hairs. On the other hand, most chemotherapy agents shorten anagen, producing a temporary balding con- dition. The condition of the Guinness long-hair titleholders is another disorder that increases the timespan of anagen, most likely involving the hormone testosterone. Minoxidil and finasteride, two medications developed for other purposes, were found in early clinical studies to produce long terminal hair growth as a side effect. These drugs are now being sold by Upjohn and Merck, respectively, either to help prevent hair loss or to grow hair for persons concerned with baldness. Hair cutting and hair length. Hairstyles and hair cutting are related to societal trends and our perception of beauty. Thus, psychological factors are very important to hair length, because the hairstyle that we select determines the length that we choose to cut our hair, and how we cut our hair is probably the most important factor that determines hair length for most persons today. Hair damage/breakage and hair length. For long hair and for very curly to kinky hair, breakage can be an important factor affecting hair length. Some of the primary causes of hair breakage are chemical treatments of hair and how curly the hair is, coupled with how we wash and comb it or brush it out. Bleaches, permanent waves, and hair straight- eners do damage hair. However, when these treatments are applied properly, they should not produce significant breakage. When these treatments are not applied properly or when combinations of these treatments are used, significant breakage can occur. Extremely curly or "kinky" hair is often very oval-shaped and behaves more like fragile, fine hair. Excessive tangling can occur with kinky hair and high combing forces are encountered. Therefore, extreme care must be taken to derangle or to minimize aletan- gling of this type of hair or excessive breakage will occur. As a consequence, long, very curly hair from African-Americans (12 inches or longer) is almost impossible to purchase in bulk from hair dealers, but Caucasian or Oriental hair 12 to 24 inches in length is rather easy to obtain. Thus, a great deal of experimental research for very curly or kinky