Detergents and soaps

Philip is doing laundry. But when he loads the clothes into the washing machine, he realises he has no more laundry detergent. Hm, could he maybe use soap instead? Soaps and detergents are substances that remove dirt from different surfaces — skin, clothes, dishes, and other solids. Soaps and detergents are quite similar.

They all dissolve in water, and contain substances known as surface active agents — or surfactants. These substances help lower surface tension, which helps wet the surface and remove dirt. Are there any differences between detergents and soaps? Is one better for cleaning certain things than the other? The main difference between soaps and detergents is actually the type of surfactants they contain and the way they are obtained.

The basic ingredient in soaps is oil or fat. Oils and fats include substances known as fatty acids. To make soap, fatty acids are mixed with a water soluble base - an alkali — such as sodium or potassium hydroxide. Then, a chemical reaction takes place, known as saponification. The result of this reaction is an alkali salt of a fatty acid — which is the chemical term for soap.

So, the basic ingredients of soap surfactants are of natural origin, and they break down naturally. They are biodegradable. Natural soaps are usually mild, which makes them perfect for removing dirt and bacteria from your skin. And they dissolve well in warm water. But in cold water or in hard water that contains many minerals, they tend to form soap scum.

This might leave residue on your clothes, or even cause damage to the washing machine over time. That's why, when doing laundry, we usually use detergents. Detergents are a whole range of different products that contain synthetic surfactants. As opposed to soaps that have been around since ancient times, detergents were first developed around the First World War. Shortages of fats and oils caused by the war, led people to look for synthetic alternatives to soaps.

Many detergents are based on by-products from the petrochemical industry. Detergents typically have more ingredients than soaps, and contain different additives that make them work precisely as desired. For instance, laundry detergents might contain brighteners that help clothes remain white, enzymes that break down stains and dirt more effectively, or ingredients that soften hard water. Detergents can also be used for a wider range of purposes than soaps. By adjusting the ingredients, detergents can be made for degreasing, disinfecting surfaces, or bleaching.

Synthetic detergents also dissolve well in hard and cold water, so they work better than soap for washing clothes. However, detergents are usually harsher than soaps. Some might even contain substances that are toxic or can cause chemical burns. So, they need to be used with more caution. Unlike soaps, most synthetic detergents don’t break down naturally, so they are not biodegradable.

So, both soaps and detergents include surface active agents that help remove dirt. Surfactants in soaps are of natural origin and are based on salts of fatty acids. Those in detergents are synthetic. Detergents can have a wider range of applications, and can be made to serve a very specific purpose. In most cases it’s best to read the label, and see what the product is meant to do.

This way you can choose the right product for the job. If you want to keep your clothes and washing machine in good condition, Philip, better skip the soap and take a walk to the store.