AKA: Aqua, Eau
Water is the most frequently used ingredient in skincare products. It is present in all emulsions and in other water-based products, such as hydrogels and other cosmetics jellies.
Water is such a common ingredient for a couple of reasons. First, it is relatively inexpensive compared to other ingredients. Second, it makes an excellent solvent for many other materials. Not everything dissolves in water, but many ingredients do, including everything from common glycerin and hyaluronic acid to more unusual ingredients like willow bark extract.
Water is compatible with most classes of ingredients – everything besides oils and silicones, and even this incompatibility can be overcome with the use of emulsifiers and surfactants.