A History of Soap and Detergent

Podcast Transcript

Sometime in the last 24 hours, most of you have used soap or detergent, either directly or indirectly.

Soap, like many other things, was most likely discovered by accident thousands of years ago.

Fast forward to today, and these products are used for cleaning almost everything, from our bodies to cars to dishes.

Soaps and detergents, despite being similar products that serve similar purposes, approach their tasks slightly differently and are used in different circumstances.

Learn more about soap and detergent, how they were developed, and how they work on this episode of Everything Everywhere Daily.

Soap and detergent are so ubiquitous in the world that we rarely even think about them. They are used for cleaning and hygiene, and most of us may have never even gone more than a few days without using them.

Yet, there was a time when people spent their entire lives without using them.

We don’t have any details as to when humans first invented or discovered soap, but it was likely an accidental discovery that occurred thousands of years ago.

It wasn’t soap exactly as we think of it today, but it would have been soap-like.

It probably happened when melted animal fat was mixed with wood ash from a campfire and mixed with water.

I’ll get into the chemistry involved in a bit, but that simple mixture had the components required to create a soap-like substance.

The earliest actual evidence we can point to of a soapy substance comes from ancient Babylon around 2800 BC, where archaeologists found clay cylinders containing a soap-like mixture of fats and ash. However, this wasn’t quite soap as we know it. It was likely used more for cleaning wool and cotton for textile production rather than personal hygiene.

The ancient Egyptians developed their own cleaning methods around 1500 BC, mixing animal and vegetable oils with alkaline salts. They understood that cleanliness was connected to health and religious purity, which drove innovation in cleaning methods.

Meanwhile, the Romans were experimenting with a substance they called “sapo,” which gives us our modern word “soap.” According to legend, this was discovered when fat from sacrificial animals mixed with wood ash on Mount Sapo, which created a substance that made washing clothes easier in the river below.

Mount Sapo probably didn’t actually exist, but the story of accidentally discovering that the mixture of fat and ash cleaned clothes might have a bit of truth to it, and it was probably something that was discovered independently multiple times around the world.

These ancient peoples were unknowingly performing a chemical reaction called saponification. When fats, which contain fatty acids, combine with strong alkalis, such as those found in wood ash or other sources, they form soap molecules that have a unique structure.

Alkalis are a type of base, which is the opposite of an acid. The alkalis used in early soap usually came from potassium, sodium, or calcium hydroxide. This is what the ash brought to the mixture with the fats.

One end of the soap molecule loves water which is called hydrophilic, while the other end loves hates water, called hydrophobic.

The hydrophobic end of the molecule readily attaches to oils, grease, and dirt that are not soluble in water because its not water in a pool of water.

When soap is added to dirty, oily surfaces and then agitated in water, the hydrophobic ends of many soap molecules latch onto the grease particles, while the hydrophilic ends stick out into the surrounding water.

As this happens, the soap molecules surround bits of oil or grime in the form of tiny spheres called micelles. Inside a micelle, the grease is trapped at the center, protected from the water by the soap molecules. Because the outside of each micelle is hydrophilic, the whole structure can now be suspended and rinsed away in water.

Soap allows oil and water to mix to form an emulsion.

In addition to emulsifying oils, soap also lowers the surface tension of water, allowing it to spread and penetrate more easily into fabrics, skin, or surfaces, which helps lift dirt away.

The combination of emulsification and reduced surface tension explains why rinsing with plain water isn’t as effective as washing with soap.

During the medieval period, soap-making evolved from accident to art. The Islamic world, particularly in cities like Aleppo and Damascus, became centers of soap production. They developed sophisticated techniques using olive oil and bay oil, creating what we now call Aleppo soap – one of the first hard soaps that could be stored and traded over long distances.

In Europe, soap-making guilds emerged in France, Italy, and Spain. The famous Marseille soap, made from olive oil and sea salt, became a standard that influenced soap-making across the continent. However, soap was still a luxury item. Most people used alternatives like sand, ash, or simply water for cleaning.

Medieval soap makers didn’t invent entirely new chemistry, but they refined techniques, experimented with different oil combinations, and developed better methods for controlling the saponification process.

The 18th and 19th centuries brought dramatic changes that transformed soap from a luxury to a necessity. Several key developments converged to make this possible:

First, in 1791, French chemist Nicolas Leblanc invented a process for producing soda ash, also known as sodium carbonate, from salt, making the alkali component of soap more affordable and readily available. This was crucial because previously, alkalis had to be laboriously extracted from the ash of plant material.

Then, in 1823, another French chemist, Michel Chevreul, figured out the actual chemistry behind saponification. He demonstrated that fats are composed of glycerin and fatty acids, and that soap formation involves splitting these apart and recombining the fatty acids with an alkali. This scientific understanding enabled soap makers to control their process with greater precision.

The Industrial Revolution brought mechanization to soap production. Companies like Procter & Gamble, founded in 1837, and Lever Brothers, founded in 1885, began mass-producing soap using steam-powered machinery.

Of interest is the development of a particular brand of soap, Ivory soap. According to legend, the floating nature of Ivory soap was discovered by accident in 1878. A worker supposedly left a soap-mixing machine running too long, whipping excess air into the batch. When the soap hardened, it was lighter and could float in water. Customers liked this feature because it was easy to find the bar in a bath or laundry tub.

It is here that the second subject of this episode enters the discussion: detergents.

Before I get into detergents, I should explain one of the major problems with soap: hard water and soap scum.

In hard water, there are magnesium and calcium ions. These can latch onto the hydrophobic ends of soap molecules, rendering the soap molecule unable to create micelles with dirt and oil.

The result is what we know as soap scum, which can often accumulate on the sides of your bathtub or in your shower. This is a bigger problem, the harder the water you are using is. Hard water is water with a high amount of dissolved minerals, such as magnesium and calcium.

If you wash in hard water, it is much more difficult for soap to develop a lather. A traditional solution to this problem was the use of washing soda, also known as sodium carbonate. Washing soda would soften the water, allowing the soap to work more effectively.

The early 20th century witnessed the emergence of synthetic detergents from German chemical research. During World War I, Germany faced shortages of fats needed for soap production, spurring chemists to develop alternatives. They created synthetic cleaning agents from petroleum and coal tar derivatives.

The real breakthrough came in the 1930s when chemists at Procter & Gamble developed the first synthetic household detergent.

So, what exactly is a detergent, and how is it different than soap?

Detergents are basically synthetic soaps. They function in a manner similar to soaps. The detergent molecules have both hydrophilic and hydrophobic ends, similar to soaps, and they form micelles around dirt and oil just like soap.

However, in detergents, the hydrophobic end doesn’t want to connect with magnesium or calcium in hard water. That means that detergents, unlike soap, don’t produce soap scum and leave a residue behind.

World War II accelerated detergent development as fats and oils were needed for the war effort. Synthetic detergents became not just alternatives to soap, but in many cases, superior cleaning agents. They worked better in cold water, didn’t leave residue, and could be formulated for specific cleaning tasks.

As the use of detergents increased dramatically, a problem arose.

Starting in the 1940s and 1950s, detergent makers added phosphates, usually sodium tripolyphosphate. They acted as builders, which meant they softened water, boosted cleaning power, and helped suspend dirt.

This made detergents with phosphates very effective, especially in areas with hard water.

When household wastewater entered rivers and lakes, the phosphates didn’t break down; they enriched the water with nutrients.

This might sound like a good thing, but it wasn’t.

These excess nutrients fueled the explosive growth of algae in lakes and rivers. Thick mats of algae blocked sunlight from penetrating the water, disrupting aquatic ecosystems. When algae died and decomposed, the process consumed dissolved oxygen, suffocating fish and other aquatic life.

Lake Erie was famously declared “dead” due to algal overgrowth.

Most consumer detergents worldwide are now phosphate-free, though some industrial and institutional cleaners still use them in controlled contexts.

I’d like to give some attention to a special type of product that most of you are also familiar with: shampoo.

If you remember back to one of my episodes on the origin of words and phrases, the word shampoo comes from India. It originally referred to an herbal product you put in your hair and had nothing to do with soap or cleaning.

For much of the 19th century, people washed their hair with bar soap or homemade soap solutions. While it did clean, it often left hair rough, sticky, or dull because of soap scum from hard water. Still, commercial “hair soaps” and perfumed wash solutions began to appear.

By the late 1800s, manufacturers marketed liquid hair cleansers under the name “shampoo.” These were essentially stronger soap solutions, sometimes mixed with herbs or fragrances; however, they still had the same problem with soap scum.

In the 1930s, modern liquid shampoo became popular in the United States. The first widely marketed liquid shampoo in the U.S. was Drene, introduced by Procter & Gamble in 1934.

What made it different from the shampoos that came before it is that it was a detergent, not a soap.

Most shampoos today contain a blend of surfactants, which are a form of detergent.

Detergents enable shampoos to be effective in hard water, offer adjustable strength that ranges from strong degreasers to ultra-gentle baby shampoos, and can be customized with conditioners, fragrances, and additives.

Simple soaps are actually relatively simple to make. There are numerous artisans who create and sell soaps at local markets worldwide. Soap can literally be made in your kitchen.

Detergents, on the other hand, are more complex and are typically produced at scale using sophisticated equipment.

The problems that the people in Babylonia faced almost 5,000 years ago are not that different from the problems we face today.

What has changed is our understanding and the sophistication of the soaps and detergents that we use to clean out clothes, dishes, cars, and ourselves.