Lay your dress on a flat surface. Remove excess lotion from the fabric by scraping it off with the edge of a spoon.
Sprinkle cornstarch over the remaining lotion stain to cover it completely. Allow the cornstarch to absorb the oil for 15 to 20 minutes.
Brush the cornstarch off and into the garbage.
Spray a petroleum-based stain pretreatment on the fabric. Let the pretreatment soak into the fabric for two minutes to break down any remaining grease.
Apply heavy-duty laundry detergent to the lotion stain. Gently rub the detergent into the fabric.
Launder your dress using the hottest water that is safe for the fabric. Add heavy-duty laundry detergent and 1 cup of white vinegar to the wash cycle to remove any last traces of the stain.
Check the fabric before drying your dress. If any lotion stain remains, repeat Steps 4 through 6 until it's removed.