How Does Soap Clean Hands?

Chemistry of Water, Dirt and Oil

Soap is a very useful substance that allows us to more effectively clean our hands. To understand how soap cleans our hands, you must first understand the chemistry behind water, dirt and grease. Water is a polar molecule. This means that water molecules (hydrogen and 2 oxygen) tend to separate into positive and negative ends. Now some substances, such as dirt and salt, are water soluble. This means they are able to easily dissolve in water, because their molecules have either positively or negatively charged parts (ions) that are attracted to the charges of the polar water molecules (they are hydrophilic). This allows them to become separated in the water and dissolve. Other substances, such as grease and oil, are not water soluble. This means they are not able to dissolve in water because their molecules do not contain positive and negative parts (ions), and so they are not attracted to the water molecules (they are hydrophobic). This means they do not become separated when they come in contact with water, and so they are not able to dissolve in water.

Chemistry of Soap

Soap is able to solve the problem of grease and oil's not being water soluble. This is because of the chemical composition of soap. Soap has an ionic head and a nonpolar tail. This means that the head of a soap molecule is attracted to water, and the tail is attracted to oil and grease. So when soap comes in contact with an oil, it connects the oil to the water and allows it to be washed off. Other water-soluble dirt on your hands can be washed off with only water, as mentioned above. Also, soap is able to decrease water's high surface tension, which is caused by the many hydrogen bonds that hold water together. When soap is used, water's surface tension is reduced; therefore, the water is able to spread out more, because it is not being held together as tightly by the hydrogen bonds. This allows the water to more effectively dissolve the dirt and oil on your hands.

Disadvantages of Washing With Soap

Soap has many advantages, but it also has disadvantages. One disadvantage of soap is that is removes oils, and this includes natural oils that are found on your hands. That is why, after using soap, your hands can become very dry. To solve this problem, many soaps have oils added to them that act to replace the natural oils on your hands. Another disadvantage of regular soap is that it does not kill bacteria, and after washing, some bacteria may still be left on your hands. To solve this problem, some soaps contain antibacterial substances, and those soaps are able to clean dirt and oil, and kill bacteria.