What Causes Melasma During Pregnancy? Melasma, or chloasma, is triggered by a combination of hormonal changes, genetics, and sun exposure. During pregnancy, the body experiences an increase in hormones like estrogen, progesterone, and melanocyte-stimulating hormone (MSH). These hormones stimulate melanin production, leading to pigmentation. Additionally, exposure to UV light can intensify the pigmentation process, causing…