Salad dressings can be stored in the refrigerator for up to 1 to 2 days after opening. If the weather is hot, overnight is not so good. Salad dressing, there is a fatal disadvantage that is not easy to keep, after opening it needs to be refrigerated, otherwise it is easy to deteriorate. Homemade salad dressing has no preservatives added and will keep for 2 days if refrigerated. If it goes bad, it will usually start with the appearance of mold on the surface before it starts to go bad. If you find no mold on the surface of the salad dressing, it is still usable.