päätehi

Päätehi is a Finnish word that translates to "end hair" or "terminal hair." In a biological context, it refers to the coarser, thicker, and often darker hair that grows on the human body, as opposed to vellus hair, which is fine, light-colored, and usually unpigmented. Päätehi is found in various areas of the body, including the scalp, eyebrows, eyelashes, and pubic region. It also develops in areas like the armpits and limbs during puberty, influenced by hormones.

The presence and characteristics of päätehi are largely determined by genetics and hormonal factors. During fetal development, the body is primarily covered in lanugo, a fine, downy hair. This is replaced by vellus hair shortly after birth. As individuals mature, particularly during puberty, androgens stimulate the growth of vellus hair into the thicker, pigmented päätehi in specific areas. This process, known as pilosebaceous unit differentiation, is a key secondary sexual characteristic. The density, length, and color of päätehi vary significantly between individuals and between sexes. For example, men typically have more prominent facial and body hair due to higher androgen levels. The scalp is a significant area where päätehi plays a crucial role in insulation and protection.