What exactly is soap? What is detergent? Many home cleaning products are classified as either soaps or detergents. Interestingly, many people really don’t know what these everyday words mean. However, it’s a good idea to take the time to learn, so you can understand their basic similarities and differences. That way, you can better judge what types of products will meet your personal cleaning preferences.
Soaps have a long history. They’ve been used to clean for thousands of years—at least in certain parts of the world. However, it wasn’t until the ancient Greek era and then the Roman age that soap making techniques were better understood and the product became somewhat more consistent. Later, during the Middle Ages, a number of towns in Spain, England, and France became well known as important soap-making centers. Yet, producing soap still remained a relatively slow and difficult process that usually yielded soaps of low or varying quality.
It was not until the 1800s that soap and soap-making changed much. At that time, with the emergence of modern chemistry and the industrial revolution, exact formulas, processes, and machinery were finally developed. As a result, soap manufacturing finally began to take place on a large scale. That trend continued, so that today in the U.S. there are literally hundreds of different types and brands of soap available. Despite other alternatives in the marketplace, soap remains the most popular skin-cleaning product. However, since the development of detergents, soaps are no longer commonly used for washing hair, dishes, laundry, or general housework.
By definition, soaps consist of natural animal fats and/or plant oils combined with some form of lye, usually sodium hydroxide (NaOH, which is a white, water-soluble, solid, caustic compound sometimes known as caustic soda). Soap comes in bars, liquids, flakes, and granular forms. Unfortunately, soaps used in hard water (water with a high calcium and magnesium content) create a scum known as soap curd. Soap curd is an insoluble, white, solid matter formed when the dissolved calcium and magnesium react with the fats and oils making up the soap. Soap curd reduces the effectiveness of any soap to clean well and, at the same time, creates a scum on sinks, tubs, etc. that can be difficult to remove.
Soaps are able to clean because they contain natural surfactants (surface acting compounds). Surfactants are necessary because they counter the effects of normally occurring surface tension in wash water. In water droplets that do not contain surfactants, the water molecules are much more attracted to each other than they are to the surrounding air molecules. This causes the droplets to pull in (or tense) on themselves, creating comparatively large, rubbery-surfaced spheres.
However, water containing surfactants behaves quite differently. This is because all surfactant molecules have one end which attracts water molecules (a hydrophilic polar end) and an opposite end that doesn’t (a hydrophobic non-polar end). Therefore, the presence of these “strangely” behaving surfactant molecules alters the usual attraction patterns in water droplets, which would otherwise cause them to pull tightly inward. The lowered surface tension results in relatively small water droplets having surfaces that are less rubbery. These smaller droplets can more easily form very thin sheets of water, as in soap bubbles, therefore more suds are possible. Smaller droplets are also better able to penetrate and lift up dirt particles as well as keep them in suspension. Finally, smaller droplets permit more thorough rinsing. All of these factors contribute to better cleaning.
Because the fats and oils in soaps create problems with soap scum, detergents were developed. This actually occurred fairly recently, during the 1930s, when very simple unbuilt detergents were first created. These early granular products consisted simply of one or more naturally derived surfactant compounds. Although they did reduce the water’s surface tension and didn’t form as much scum, they didn’t clean as effectively as was expected. As a result, after World War II the first modern built detergents were created and marketed. Generally, these detergent formulas contained synthetically derived surfactants originating ultimately from crude oil and additional builder ingredients. These included substances such as phosphates, carbonates, silicates, amines, zeolites, sodium EDTA, and sodium sulfates. (Minute quantities of metals such as cadmium, lead, mercury, and arsenic were also frequently present as contaminants.) These builder compounds further controlled the minerals in hard water, increased the alkalinity, and enhanced the surfactants’ capacity to lower the water’s surface tension. Eventually, other ingredients were added to certain detergent formulas, including compounds to prevent dirt particles that are suspended in the water from redepositing themselves, oil emulsifiers (compounds able to stabilize oil in water), optical brighteners (compounds able to give cleaned items the appearance of being whiter), bleaching agents, suds-controlling compounds, perfumes, and dyes.
Despite their cleaning advantages, over the years detergents have had certain problems. For example, virtually all the early detergents used surfactants that couldn’t biodegrade easily. Because of this, huge quantities of foamy suds began forming and accumulating in American sewers and waterways in the 1950s and early 1960s. Another major concern has been with certain phosphate-containing ingredients. As it turns out, when these phosphate compounds dissolve in water they release phosphorus. When the phosphorus reaches lakes and streams, it acts as a fertilizer, causing algae and other aquatic plants to proliferate much too rapidly. The resulting overgrowth, or blooms, can create unbalanced ecosystems in which algae and plants clog the surface of the water.
Fortunately, since 1965, all laundry detergents in the U.S. are now voluntarily made to be biodegradable. Also, the amount of phosphate content has been either lowered or eliminated. (Certain states and localities have completely banned all phosphate containing detergents.) To compensate for the cleaning effectiveness that has been lost through phosphate reduction or removal, a number of other ingredients (such as the optical brighteners mentioned earlier) are now commonly added.
Today, you can buy detergents in granular, gel, and liquid forms. Although most detergents contain totally synthetic formulas, a few are being made with naturally derived compounds. Because of their effectiveness, detergents are now used for most cleaning jobs. That is, except for washing skin—although there are some detergents designed to do that as well.
Should You Use Soap or Detergent?
Both soaps and detergents contain surfactants that are able to lower wash water’s surface tension. Therefore, both have the capacity to lift soil and suspend it in the water in order to clean. However, detergents have been specially designed to have these qualities enhanced—and to minimize soap scum. On the other hand, soaps tend to be made of mostly natural ingredients, while detergents generally are not. Also, soaps usually have simple formulas while most detergents contain a more complex variety of ingredients.
Of course, whether to use a soap or detergent is ultimately your own personal decision. However, for sensitive or highly allergic individuals, using any of the typically available soap and detergent brands may prove too bothersome. For such people, alternative unscented products with basic formulations in either category are often far more tolerable.