Detergents and soaps

Last updated: May 2, 2008.

When you're young, "bathtime" is another word for "torture" and a harmless block of soap can seem like an offensive weapon. Fortunately, most of us soon grow out of that little problem and learn to recognize soap and water for what they are: a perfect way to shift the daily grime.

With the possible exception of water, soap seems like the simplest thing in the world. Just splash it on your face and it gets rid of the dirt, right? In fact, it's quite a cunning chemical and it works in a really interesting way. Let's take a closer look!

Photo: Some typical household detergents. All of them, except for the soap, are liquids. The two Ecover products on the left are made with plant-based ingredients to reduce their environmental impact.

What are detergents?

Often we use the words "soap" and "detergent" interchangeably, but really they're quite different things. A detergent is a chemical substance you use to break up and remove grease and grime, while soap is simply one kind of detergent. Soap has a long history and was originally made from purely natural products like goat's fat and wood ash. Today, detergents are more likely to be a mixture of synthetic chemicals and additives cooked up in a huge chemical plant and, unlike traditional soap, they're generally liquids rather than solids. Detergents are used in everything from hair shampoo and clothes washing powder to shaving foam and stain removers. The most important ingredients in detergents are chemicals called surfactants—a word made from bits of the words surface active agents.

How detergents work

You might think water gets you wet—and it does. But it doesn't get you nearly as wet as it might. That's because it has something called surface tension. Water molecules prefer their own company so they tend to stick together in drops. When rain falls on a window, it doesn't wet the glass uniformly: instead, it sticks to the surface in distinct droplets that gravity pulls down in streaks. To make water wash better, we have to reduce its surface tension so it wets things more uniformly. And that's precisely what a surfactant does. The surfactants in detergents improve water's ability to wet things, spread over surfaces, and seep into dirty clothes fibers.

Surfactants do another important job too. One end of their molecule is attracted to water, while the other end is attracted to dirt and grease. So the surfactant molecules help water to get a hold of grease, break it up, and wash it away.

Additives

Surfactants aren't the only thing in detergents; look at the ingredients on a typical detergent bottle and you'll see lots of other chemicals too. In washing detergents, you'll find optical brighteners (which make your clothes gleam in sunlight). Biological detergents contain active chemicals called enzymes, which help to break up and remove food and other deposits. The main enzymes are proteases (which break up proteins), lipases (which break up fats), and amylases (which attack starch). Other ingredients include perfumes with names like "limone", while household cleaning detergents contain abrasive substances such as chalk to help scour away things like burned-on cooker grease and bath-tub grime.

A brief history of soaps and detergents

• 600BC: Historians think people have been making soap for around 2000 years, even since the time of the Phoenicians (an early Mediterranean civilization).
• 1790: Soap was an expensive luxury until French chemist Nicolas Leblanc (1742-1806) found a cheaper way of making it using salt.
• 1800s: Soap-making became popular in the United States and North America, where people mixed the ingredients in large "soap kettles". Soap kettles were used for most soap-making until World War II.
• 1916: German chemist Franz Gunther develops the first surfactant for detergents from coal tar.
• 1930s: Detergents based on surfactants were introduced in the United States.
• 1950s: Synthetic detergents are developed to counte rsoap shortages caused by World War II and soon overtake traditional soap to become our favorite chemical cleaners.
• 1960s/1970s: Concerns about water pollution from detergents building up in rivers and seas led to the development of the first biodegradable surfactants.