Soaps are everywhere. From taking a shower to washing our clothes, from shampooing our hair to scrubbing our utensils – the ‘cleaners’ we use come in so many shapes and forms. Are they similar to each other? Are they different? Is it a little bit of both? Let’s find out!
Since the key role played by these products – whether soap or detergent – is to clean, it is important to understand how they function. Water and other liquids have a property called surface tension, which enables them to minimize their surface area when at rest. In the context of cleaning, the interaction surface between any ‘dirt’ and the water we use to wash it, would be at its lowest by default. This would inhibit the water from effectively washing away any grease or stains.
Sounds like a bad thing right? It is!
Enter – surfactants; short for surface-active agents. Surfactants lower the surface tension of water, or increase the interactive area between dirt and water. Their molecules contain a lipophilic (fat-loving) end that attaches to grease or dirt, and a hydrophilic (water-loving) end which gets attached to water. As we rinse, the dirt molecules attached to water through the surfactant get washed away.
This is the key point of similarity between soaps and detergents. Whether it is laundry detergent, floor cleaner, toothpaste or shampoo – the underlying principle remains the same. A bipolar molecule bringing together water and dirt, and the three of them leaving together. Quite interesting right? Wait till you hear the differences!
How they vary
Don’t worry, you aren’t washing your hair with laundry detergent! The broad manufacturing process for both soaps and detergents is called ‘saponification’, where a fat molecule is reacted with a strong base. Fat, made of triglycerides, is composed of three fatty acids (hence the prefix “tri-“) connected to one glycerin (hence “glyceride”).
Soap and Glycerin are the key products of this reaction.
Two conditions have to be met for the soap (above) to be a ‘true soap’
- The starting material has to be a triglyceride or fatty acid, most commonly plant or animal based
- The synthesized glycerin has to be left in the soap. In most personal care products like soaps and shampoos, this is the critical factor that gives them moisturizing properties.
By extension, detergents are defined as those ‘soaps’, where:
- The starting material is a hydrocarbon chain (which is a fraction of a fatty acid/triglyceride/whole fat) from either a petrochemical (derived from petroleum), or an oleochemical (derived from fat and oils)
- The synthesized glycerin is removed and sold separately. This makes detergents relatively drying and more suited for home care products.
This is quite a simplified overview, and many variations can exist – depending on the oil used, the manufacturing process and the degree of glycerin separation. An interesting example is Sodium Cocoyl isethionate – a coconut oil based surfactant which is technically a detergent, but very well suited for personal care products due to its fatty acid composition. It can also be supplemented with a host of oils and butters to manufacture nourishing shampoos and bathing bars.
It is important to know this distinction because in labeling, detergents should not be called soaps.
If the resulting product:
> Is not a sodium or potassium salt of a triglyceride or fatty acid
> Is synthesized from hydrocarbon chains
> Or has had glycerin removed – it is not a true soap.
It may be a gentle detergent, but it is not a soap. And that’s ok 🙂