A Detergent is a cleansing agent and a synthetic substance other than soap. A detergent contains an active agent (called surface active agent or surfactant) that wets the fabric, emulsifies oily metal soubise grime and keeps the soil in suspension. A liquid detergent is a surfactant or a mixture of surfactants with "cleaning properties in dilute solutions." These substances are usually alkyl benzene sulfonates, a family of compounds that are similar to soap but are more soluble in hard water, because the polar sulfonate (of detergents) is less likely than the polar carboxyl (of soap) to bind to calcium and other ions found in hard water.