Hydrosols are aromatic water remaining made from the distillation of fresh flowers, leaves, fruits, and other plant materials. They're a byproduct of the essential oil manufacturing process. Steam distillation results in two complementary products - the essential oil and the hydrosol. The difference is that hydrosols are mostly aromatic water. This means they're much less concentrated than essential oils. They also have a softer, more subtle scent. Hydrosols are often used in skin care or aromatherapy products. While they've also been used for medicinal purposes, more research is needed to prove their effectiveness.