Of all the skin cleansing products available today, soap, specifically the kind that comes in bars, is by far the most popular and common. Virtually everyone has used soap at some point in their lives, and the vast majority of us regularly keep some form of it at home [source: The Global Public-Private Partnership for Handwashing with Soap]. Soap's prevalence isn't all that surprising, especially considering it's been mankind's top pick for skin cleansing and skin care for nearly 5,000 years [source: The Soap and Detergent Association].
Soap is created through a process called saponification, which is the chemical reaction that occurs when a fat, such as tallow (beef fat), and an alkali, such as lye, are combined [source: Encyclopedia Britannica]. Natural oils, such as olive oil, can be added to this mixture or used instead of animal fats, if desired.
Like detergents, soap is a surfactant, which means that it helps lower the surface tension of water. Dirt and oils that won't budge during a quick rinse can be easily wiped away by soap because it allows the water to penetrate and spread more thoroughly over the surface of your skin.
In fact, soap does its job a little too well. While the surfactant nature of soap allows it to help wash dirt and grime off your body, it also removes the oils naturally secreted by your skin. Frequent washing with soap can produce dry, cracked skin, which, besides being uncomfortable, may also lead to infections [source: Leffell].