Hydroquinone, tretinoin, and hydrocortisone work together to treat melasma, a skin condition that causes dark spots on the face. Hydrocortisone works by acting inside skin cells and inhibits the release of certain chemical messengers in the body that cause redness, itching and swelling. Hydroquinone works by decreasing the amount of melanin (a skin pigment) that is responsible for the darkening of the skin.