What chemical messenger promotes changes such as the formation of facial hair?

Testosterone is the chemical messenger responsible for promoting the development of facial hair, particularly during puberty in males. It is an androgen, which is a class of hormones that play a role in the development of male characteristics. In the presence of testosterone, hair follicles in certain areas of the face are stimulated to grow thicker and longer hair, which leads to the development of facial hair such as beards and mustaches.

Additionally, testosterone influences other secondary sexual characteristics, such as increased muscle mass and changes in voice, all of which contribute to the maturation of male physical traits. While dihydrotestosterone, a derivative of testosterone, also plays a significant role in hair growth, particularly in areas like the beard, it is testosterone that initiates the overall hormonal changes that lead to these developments.

Estrogen and progesterone are primarily involved in female reproductive functions and secondary sexual characteristics related to femininity, rather than promoting facial hair growth.