Laundry Soap vs Detergent: What’s the Difference?

Laundry detergent and laundry soap are terms many people use interchangeably without thinking too much about it. I always assumed they were the same thing, and perhaps you did too. 

But in researching sustainable household cleaning options, I began to wonder, Is there actually a difference between the two? 

To get to the bottom of it, I spent a week investigating the two types of cleaners to discover the difference. Here’s what I found.


What is Laundry Soap?

Laundry soap is used with water and is made with natural, biodegradable ingredients, such as plant oils and animal fat mixed with alkali salts (lye), and may also contain essential oils or colorants. It is commonly found in bar form, as well as liquid. 

Soap-making has been around since the beginning of time—well, maybe not the very beginning, but it has been around for an extremely long time. Soap-making is practiced all around the world, in slightly different ways, with slightly different ingredients, but when it comes down to it, all soap is made with the same basic natural ingredients.

What is Laundry Detergent?

Laundry detergent is a store-bought solution for washing your clothes that usually comes in powder or liquid form. Detergents were invented to mimic soap and are made with a list of man-made ingredients, such as sodium lauryl sulfate, phosphates, surfactants, bleach, dyes, and synthetic fragrances, just to name a few.

A little over a hundred years ago, there was no such thing as detergents. It may feel like laundry detergents have been around for a long time, but they are actually a fairly new product. Back during World War I, when items became harder to get—like soap— people invented detergent to take its place. Detergents clean away dirt from laundry like soaps do, but they use man-made, chemical ingredients to do so.

How Do They Work?

Laundry detergents and soaps are made up of a whole lot of ingredients that contain molecules. The most important of these molecules are called surfactants, otherwise known as surface active agents. They have a water-loving head on one end and an oil-and-grease-loving tail on the other. 

When activated, one end (the oil-and-grease-loving tail) will attach itself to the oil and dirt in your clothing, while the water-loving end attaches itself to the water to pull the molecule out from your clothing, along with the oil and dirt that’s attached to it, washing it all away.

What’s the Difference?

Both soap and detergent are made with the same outcome in mind, namely, to clean clothes, and they do just that. But they have several significant differences. 

Ingredients

The different key ingredients in laundry soap and laundry detergent set them apart the most. 

Soap is simple and natural and made with fewer ingredients. It consists of animal fats (lard, tallow) or plant/vegetable oils (olive, coconut, soy, hemp, jojoba, etc.) and is mixed with water and lye to make soap. Lye is important for soap-making because the lye and oils react with one another, causing saponification—that’s when we get soap. Other than fatty acids, lye, and water, some soaps may contain coloring and scents, and depending on the specific ingredients, because it is natural, it could contain preservatives to keep it from going bad sooner. 

Detergent is a lot more complicated than soap, made up of a long list of synthetic compounds. Most of what makes up laundry detergents are chemicals, with the worst of them being dioxane, phosphates, optical brighteners, and surfactants. These chemicals can have a negative impact on our health and the environment around us. A lot of detergent brands are trying to reduce their environmental impact by eliminating harsh chemicals from their ingredients, but most still use many synthetic ingredients.

Water requirements

Soap and detergent perform on different levels when it comes to water quality.

Soap reacts poorly with hard water. When mixed with hard water, soap does not produce the good lather that you need for a thorough cleaning, and when soap reacts with some of the minerals in the water it can cause a buildup of soap scum as well. 

Detergent isn’t like this and can work in both soft water and hard water. Because detergent ingredients are man made, they’re formulated to work for everyone the same way no matter what kind of water you have.

Temperature requirements

Both detergent and soap need water in order to dissolve and activate cleaning power, but they perform differently in different temperatures.

When it comes to soap, wash-water temperature is very important. Soap needs warm water, or even hot water, so that it can dissolve and wash properly. Undissolved laundry soap can cause soap scum to build up inside your washing machine and even leave soap scum residue on your clothing. 

Unlike soap, laundry detergent will clean your clothing in any water temperature. Manufacturers even market laundry detergents that are specifically made for use in cold water for those who have decided to cut back on their hot water usage.

Stain removal

The top qualities you usually look for when buying a laundry product are to clean your clothing and remove odors, as well as eliminating stains.

Laundry detergent is the most effective cleaner for stain removal and brightening your clothes. Don’t get me wrong, soap is amazing at cleaning your laundry of dirt and oil too, but the science and technology that go into developing detergents now alter different components into stain-fighting powerhouses.

Rinsability

While laundry soap and laundry detergent are designed to perform similar roles, their individual ingredients mean they function differently. 

Soap rinses from your laundry better than detergents. If you ever add too much to your washing machine, soap will always rinse clean from your clothing, but detergents can leave residue behind

Detergents contain synthetic oils that hold in its fragrance, but those end up clinging to your clothing and don’t fully come out in the rinse cycle. That’s great if you want your clothes to smell good, but what about all that dirt and residue that’s also not getting rinsed out? All that leftover laundry detergent in your clothing can be absorbed into your body, and irritate sensitive skin too.

Environmental impact

Detergents have a big impact on our freshwater. All those synthetic chemicals that are powerful enough to zap stains, odors, and grime out of existence don’t have the same positive effects on water sources and delicate ecosystems. These harmful chemicals can ruin aquatic habitats and contaminate drinking water. This article from Victoria University of Wellington’s Environmental Science Department explains these environmental concerns.

Although soap is biodegradable and a more eco-friendly cleaner, a tiny percentage of soap can contaminate water. In saying this, soap is still A LOT kinder to the environment than detergent. 

Which Is Better?

You might still be wondering which is better. Well, depending on your specific laundry needs, both laundry soap and laundry detergent may stand out to you as the best.

The case for soap

Soaps are made with all-natural ingredients, and those natural ingredients are more gentle on your body and the environment. 

The production of soap is also less harmful to the environment than the production of detergent. Because of soap’s simpler form and raw materials that need less processing, less pollution occurs than with detergent production, wherein almost every ingredient is concocted before they even begin making the detergent itself. 

Laundry care expert Patric Richardson never uses detergent, but instead sticks to the safer option of laundry soap. If all-natural ingredients and sustainability matter most to you, perhaps laundry soap is the better choice for you as well. 

The case for detergent

Both soap and detergent are great cleaners, but detergent’s man-made ingredients are easily altered by chemists to make it even more powerful. Therefore, detergent can get your toughest stains out better than soap can. 

But, really, is it worth it to have synthetic cleaners strong enough to dissolve away a stubborn stain rubbing on your body all day? Are all those chemical cleaners in your detergent worth it? 

If your main goal is stain-fighting power, it might be. But not all detergents are created equal, and you don’t have to choose the harshest one. Some are gentler than others on your clothes and the environment. You can find substitutes for store-bought detergent or even make your own

Only you know your values and needs, so only you can determine which is better for yourself and your family. 

How Do You Tell Soap From Detergent?

Believe it or not, a lot of cleaning products marketed as soaps are not actually soap at all, but detergents. And some detergent companies label their products as laundry soaps to satisfy trends in all-natural manufacturing. On the other hand, some laundry soap companies label their products as detergents to appeal more to people looking for laundry detergent. 

So if you really want to know what you’re buying, the best thing you can do is read the ingredients.

Alternatives to laundry soaps and detergents have begun to emerge, including laundry pods and, more recently, eco-friendly laundry sheets, providing a sustainable way to wash your clothes. For more information, check out my article comparing the top eight laundry sheets.

Conclusion 

So there you go, now you know that there is, in fact, a difference between soap and detergent. Laundry detergents and laundry soaps are made to achieve the same outcome—washing your laundry—but when it comes to ingredients, performance, and sustainability, they’re quite different.

Now that you’re more aware of the main differences between soap and detergent, the next time you’re at the store you can make better choices about what you’re putting in your washing machine, sending to your local water sources, and absorbing into your clothes and skin.