Soap is a cleansing agent which, when dissolved in water, removes dirt from soiled surfaces. Made from animal fat and wood ashes, soap is one of the earliest chemical inventions and was first used as a salve or ointment. Many ancient cultures made and used soap, the Sumerians as early as 3000 B.C. The ancient Egyptians used a soap-like paste to treat skin disease.

The Romans learned about soap from conquered peoples, perhaps the Celts or the Gauls. In his Historia naturalis the Roman naturalist Pliny the Elder (ca. 23 A.D.-79 A.D.) mentions soap used by the Gauls as a hair dye and salve. The Greco-Roman physician Galen (ca.130-c.200) wrote about soap as a medication and--for the first time--as a cleanser in one of his treatises published in the second century A.D. The Arab alchemist Jabir ibn Hayyan (Geber) also...