What hormone is responsible for stimulating skin pigmentation?

Melanocyte-Stimulating Hormone (MSH) is the correct answer because it is specifically produced by the pituitary gland and plays a crucial role in regulating skin pigmentation. MSH stimulates melanocytes, the cells in the skin responsible for producing melanin, which is the pigment that gives skin its color. When MSH is released into circulation, it binds to receptors on melanocytes, resulting in increased melanin production. This process is important not only for pigmentation but also for the protection of skin from ultraviolet radiation.

In contrast, prolactin primarily regulates milk production in lactating women and has no direct role in skin pigmentation. Thyroid hormones, while they can influence metabolism and overall skin health, do not specifically stimulate melanin production or melanocyte activity. Adrenocorticotropic Hormone (ACTH) is involved in stimulating the adrenal cortex and the production of corticosteroids, but it does not have a primary function in regulating skin pigmentation.