What pigmentation disorder, commonly referred to as the butterfly mask of pregnancy, is characterized by brown spots on the face?

Chloasma, commonly known as the "mask of pregnancy," is a pigmentation disorder characterized by the appearance of brown spots on the face, particularly across the cheeks, forehead, and upper lip. This condition often arises due to hormonal changes during pregnancy, leading to increased melanin production in these areas. The hormonal fluctuations, particularly involving estrogen and progesterone, stimulate melanocytes (the cells responsible for skin pigmentation) to produce excess pigment.

Chloasma is most prevalent among pregnant women but can also occur in non-pregnant women and occasionally in men, particularly with hormonal changes from medications or other health conditions. The brown patches typically fade after childbirth or the cessation of hormonal influences but can be influenced by sun exposure, which can exacerbate pigmentation.

Other pigmentation disorders mentioned differ in their characteristics; for instance, ephelides (freckles) are small, benign spots that appear primarily due to UV exposure, while lentigo refers to age spots often resulting from sun damage over time. Vitiligo, on the other hand, is an autoimmune condition that causes depigmentation patches on the skin, which is entirely different from the increased pigmentation seen in chloasma.