Hydrophilic substances are materials that have an affinity for water. They can easily dissolve or mix with water due to their polar nature, which allows them to form hydrogen bonds with water molecules. Common examples include sugar, salt, and alcohol. These substances are often found in biological systems, where they play crucial roles in processes like nutrient transport and cellular interactions. In contrast to hydrophobic substances, which repel water, hydrophilic substances are essential for various chemical reactions and biological functions. Their ability to interact with water makes them important in fields such as biochemistry and environmental science, where understanding solubility and interactions is vital.