A
detergent is a
surfactant or a mixture of surfactants with "cleaning properties in dilute solutions." These substances are usually
alkylbenzenesulfonates, 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. In most household contexts, the term
detergent by itself refers specifically to
laundry detergent or
dish detergent, as opposed to
hand soap or other types of cleaning agents. Detergents are commonly available as powders or concentrated solutions. Detergents, like soaps, work because they are
amphiphilic: partly
hydrophilic (polar) and partly
hydrophobic (non-polar). Their dual nature facilitates the mixture of hydrophobic compounds (like oil and grease) with water. Because air is not hydrophilic, detergents are also
foaming agents to varying degrees.