What is the Difference between Soap and Detergent?

Castellet-Soap Is there a difference between soap and detergent? Both clean what they are made to clean. But, yes, there are  differences. They come from different sources. They are different chemically. And they are put to different uses. An example of each is provided, below.

Soap

There are a variety of soaps. A soap is the metal salt of a fatty acid.

A fatty acid is an organic compound most often of animal or plant origin. A fatty acid contains a long-chain aliphatic carbon skeleton (with or without branches) plus a carboxylic acid group (-COOH) at its end.



The metal may be an alkali metal such sodium (Na) or potassium (K). These metals are found in the first column of the periodic table of the elements. Or, the metal can be an alkaline earth metal, such as calcium (Ca) or magnesium (Mg). These metals are found in the second column of the periodic table of the elements.

difference between soap and detergent
Laundry Day

Detergent

Detergents have some similarities. But are often of synthetic origin. They are not made insoluble by hard (mineralized) water. Instead of a carboxylic acid group, detergents contains a more intensely ionic group. It may be a sulfate or a sulfonate group (-OS(O)₂-OH).

difference between soap and detergent In addition, detergents can include aromatic rings. Detergents can also be used as surfactants and foaming agents.

There are even detergents that dissolve in solvents other than water, such as gasoline. These often include nitrogen in their formulation. The nitrogen compound frequently includes a ring as part of its structure. Such compounds are not only detergents, but dispersants.

Example Difference Between Soap and Detergent

difference between soap and detergent

An example of a soap is potassium palmitate:

CH₃(CH₂)₁₄-COO⁻ K⁺

An example of a detergent is sodium lauryl sulfate:difference between soap and detergent

CH₃(CH₂)₁₂-OS(O)₂-O⁻ Na⁺

Note: You might also enjoy Ammonia and Bleach – Why a Bad Choice?

References: ← Back to Food-Health
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20 thoughts on “What is the Difference between Soap and Detergent?

  • In the UK, most shampoos and shower gels are detergents, as is what we term “washing up liquid”, which I think Americans call “dish soap”. My granddaughters love bubble bath (detergent) but it is so hard to get the bubbles to drain after the bath. I have found that washing your hands with a piece of soap in the detergent water helps get rid of the bubbles. They seem to work against each other!

  • Styra Avins

    In my experience, detergent is much better at dissolving fats, without leaving any residue. If you wash your hair with soap, you will find it very difficult to rinse thoroughly. If you have been in poison ivy and need to wash the irritant oil off your skin, detergent is far more effective than even soap made with lye. (East coast of the USA, I have years of experience on this point!). On the other hand, soap is much nicer! I use brown soap for wiping my kitchen sink and surfaces. But my question is still, in what way does detergent work differently from soap? What is the mechanism of the soap molecule vs. the detergent molecule?
    Thank you.

    • G Namchuk

      I would also like to know the difference in the mechanisms of the two different types of molecules (soap vs detergent), so am asking one of you/someone to reply to that question. I just finished reading an article about garlic used as an insect repellant which specified using a soap rather than a detergent (for dogs), which is why I was looking for the difference between the two. So, while I liked the article, I don’t really have an answer to my original query about why a soap may be preferable to use in certain applications over a detergent. Also, – separate topic – What is the purpose of the italicizations in your article? The italicized words in your article seem to need definitions, but on my iPad there are no hyperlinks.

  • Patti Crossley

    Molecularly, how do they differ in the cleaning process? My Dad once told me that one of them wraps the dirt (I think that was the soap) and lifts it up, and the other dissolves the dirt — which is which, and is this accurate in any way?
    Thank you very much.
    Patti

    • Soap ionizes in water. The fatty portion of soap attaches to the dirt. Micelles form around the dirt, enabling it to be all washed away. Detergents are stronger, synthetic chemicals that act primarily as surfactants. They loosen the dirt from the dirty object.

  • Beth

    My small washer/dryer’s instructions say to clean the casing with soapy water or a non-solvent cleaning agent. What would a non-solvent cleaning agent be? Would they be referring to something like Murphy’s Oil Soap or a similar product without soap in the name? Do you know any common examples?

    • Murphy’s should be just fine. Although water is an excellent solvent, sometimes, as undoubtedly you know, language can be confusing! Generally solvent, in such a context, refers to something like turpentine, gasoline, an alcohol, a ketone, or other hydrocarbon substance. Some hydrocarbons can not only assist in cleaning, but in removing paint or dissolving plastic. You wouldn’t want to use those in the case you describe. It is true Murphy’s contains some glycol, but it primarily uses water. When in doubt, you can always clean a small spot that is not visible to test its efficacy.

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