Three different types of hair can be found on the body over the course of a lifetime. The first hair type, which covers the body of the fetus by about the 5th or 6th month of fetal development is called lanugo (Figure Link of lanugo on infant). Lanugo is very fine and usually un-pigmented. It is usually shed before birth but at times is still present.
Lanugo Hair on Infant. Author: Raumka at English Wikipedia (Transferred from en.wikipedia to Commons.) [CC0], via Wikimedia Commons. Link: https://books.byui.edu/-QVLY
Lanugo is replaced by an even finer hair called vellus hair. It is best described as the peach fuzz seen on the faces of children and women.
Vellus Hair. Author: By Svdmolen (Self-published work by Svdmolen) [GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/) via Wikimedia Commons. Link: https://books.byui.edu/-nWex
What we typically think of as hair is called terminal hair. Terminal hair is the hair of the scalp, eyebrows and eyelashes of infants and prepubertal children.
Terminal Hair. Author: By odder [GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/), via Wikimedia Commons Link: https://books.byui.edu/-bFwc
Beginning at puberty and under the stimulation of androgens (testosterone), the vellus hair on other parts of the body is replaced by terminal hair. In both men and women terminal hair replaces the vellus hair in the axillary and pubic regions at puberty. Additionally, in boys about 90% of the vellus hair on the arms, legs, face, chest and sometimes back is also replaced by terminal hair. In women about 35% of the arm and leg hair is replaced by terminal hair.