J. Soc. Cosmetic Chemistry, 20, 159-171 (March 4, 1969) Differences Between Adult and Children's Hair HERMAN BOGATY, B.S? $ynopsis•A review--much of it from the anthropological literature--is given on the structural, morphological, and color changes of hair on the head with aging of the subject. Children's hair is on the average finer, rounder, less frequently medullated, and lighter in color than adults' hair. Scaliness and cuticle-cortex ratio are less certainly related to age, nor is there a consistent effect reported on changes in chemical and physical properties. The physics of hair color is discussed and some limited experimental data are reported suggesting that children's hair is more transparent and is less red in hue, with a trend to higher purity. INTRODU GTION In connection with hair color studies, the technical literature on the differences between adult and children's hair was searched. While hair appearance and color were the primary concern, information on the geometry, shape, and chemistry was also uncovered. Much of the published data found appeared in literature normally not available to cosmetic scientists in physical anthropology and anatomy---and in the period between 1925 and 1945. Because the findings may be of general interest, it was thought useful to bring together in one place the information obtained and to provide a fairly complete set of references against future needs. Some brief comment on background and terminology may be helpful. Criteria for classification of hair have included gross size, time of appearance during the life span, and structural variations. Lanugo, or primary hair, is characteristic of the fetal stage of life. It tends to be fine and silky, is nonmedullated and may be considerably pigmented. Secondary, or vellus, * The Toni Company, Chicago, Ill. Present address: Warner I.ambert Research Institute, Morris Plains, N.J. 07950. 159

160 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS hair is short, fine, and usually unpigmented the downy underfur of some mammals and the fine body hair of children and women are probably characteristic. Some authors restrict the term vellus to such fibers rather than to any type of scalp hair. The tertiary, or terminal, hair is normally considered to be long, coarse, and pigmented, and associated with the mature individual. There is considerable overlap in the various types, and on any given animal or in any specific region of the skin all types may be evident, as well as intermediate varieties. Most anthropologists view the changes that take place as developmental, whenever the transition from the primary through the terminal types occurs with increasing age (1-3). A corollary of this view is that the changes do not occur all at once, and that at any given time some fraction of the more primitive hairs may be present. Thus, Danforth (1) observes that between 6 and 21% vellus hairs may still be present in late childhood during the transition to terminal piliation. DIMENSIONS AND MORPHOLOGY Cross-Sectional Size and Shape o[ the Hair Both of these characteristics have usually been measured together on the same samples. In an early paper, Wynkoop (4) concludes that "hair shaft diameter bears little or no relationship to the age of the individual, though there seems to be a rough correlation . . . with age group of individuals .... " Examination of her data indicates that the 0- to 9-year age group of hair samples does have substantially finer hair than the samples of older groups measured. Trotter and her coworkers (5-7) investigated these hair characteristics more thoroughly by using a somewhat better technique. Some data from these sources, regrouped and rearranged, are given in Tables I and II. These results show the average increase in linear density and of cross-sectional area with age at least through the teen years. There is also a suggestion o[ a modest decline with older age groups. The ellipticity, as measured by hair index, does not in these data correlate with age. It is emphasized that these results are averages and that each head contains individual fibers of a wide range with much overlap among the age groups. In view of the subject-to-subject variability, the results from two additional papers by this group of workers are more conclusive (8, 9). The hair index and size of a small group of children were followed by sampling their heads on a regular time schedule from birth through early teen age the data are given in Table III.