Deliquescent substances are hygroscopic, which means they have the ability to absorb moisture from the air. These substances dissolve in the absorbed moisture to form a solution. In other words, deliquescent substances become liquid when they absorb enough moisture from the air. This is in contrast to efflorescent substances, which lose moisture and become powdery, and anhydrous substances, which do not contain any water. Insoluble substances do not dissolve in a liquid, but deliquescent substances are soluble in the moisture they absorb from the air.