Final answer:
Ash was an early form of an alkali that, when mixed with oils, created a basic soap for handwashing, utilized by ancient civilizations for hygiene before modern soap was available.
Step-by-step explanation:
People once washed their hands with ashes because ash can act as an alkali that reacts with oils to form a basic type of soap. The use of ashes predates modern soap-making practices. For example, the ancient Egyptians created a soap-like substance by combining oils with alkaline salts. In Nabonidus's time, a soap recipe included ashes, cypress oil, and sesame seed oil, which was used for cleansing purposes. Similarly, the ancient Israelis made soap from the ashes of barilla plants, producing potash, a key ingredient in soap production. Therefore, washing with ash was an early form of sanitation practice before the understanding and availability of manufactured soaps.