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Sodium or potassium salts of long chain fatty acids. These detergent substances are obtained by boiling natural oils or fats with caustic alkali. Sodium soaps are harder and are used as topical anti-infectives and vehicles in pills and liniments; potassium soaps are soft, used as vehicles for ointments and also as topical antimicrobials.

The sodium or potassium salts of palmitic, stearic, or oleic acid. They are soluble in a small amount of water and the solution becomes turbid upon dilution. The aqueous solution has the property of forming an emulsion with fats or grease and so removing them from surfaces to be cleansed. The calcium and magnesium salts of the three fatty acids named are insoluble in water, consequently a precipitate is formed when the so-called hard waters (which contain calcium and magnesium salts) are treated with soap. By the addition of an excess of soap, the hardness can be removed. Soaps are found in the chyle, the blood, bile, and in the milk.