The Effects of Aging on Hair–More Than Just Amount 460 seventh month and is replaced by a coarser and longer hair which is generally replaced by an even coarser hair at about 2–3 years of age. But the data also suggests that the hair becomes coarser as the child continues to age. Table 3. Cross-sectional area and the age of Caucasian children from Trotter13 Age Statistics Calculated Average Diameter (µm)* 1 month ** 31 7 months ** 35 2 years ** 50 3 ** 55 4 59 5 60 6 63 7 64 8 65 9 66 10 66 *Diameters calculated assuming circularity **Significantly different from all other values. Lines indicate those values that are not significantly different from each other by the matched pairs test. Puberty through Adulthood for Females: The study by Otsuka and Nemoto15 on the hair of approximately 18,000 Japanese females ages 10–60 is the largest published study containing data on hair diameter and age. However, this study does not provide any experimental details, including the method for collecting hair samples, the site from which hairs were taken, nor the method of measurement. For women, this study shows that hair diameter versus age is not a linear relationship, but rather that it displays curvature increasing to a maximum near the age of 40 and then it decreases thereafter, as shown in Table 4.