Although these two are frequently interchanged, it is important to understand how they differ from each other, as hydrators and moisturizers work differently.
They both have the same goal: to help the skin get enough water and prevent it from drying (lack of oil) and/or dehydrating (lack of water).
However, hydrating does it by bringing enough water to the skin, while moisturizing locks the water molecules in the skin.
Hydrators use humectants to absorb water from the environment (or deeper layers of the skin) for the cells to absorb it.
Moisturizers prevent water from escaping the skin and support its protective barrier. These are divided into different classes, like occlusives, humectants, emollients and protein rejuvenators.