Hydroquinone + Mometasone + Tretinoin treats melasma (dark spots on skin). Hydroquinone is a skin lightening medicine. It reduces the amount of a skin pigment (melanin) that causes darkening of skin. This effect is reversible. Mometasone is a steroid which blocks the production of certain chemical messengers (prostaglandins) that make the skin red, swollen and itchy. Tretinoin is a form of vitamin A that helps the skin to renew itself more quickly.