Difference Between Soap and Detergent


Main Difference

The main difference between Soap and Detergent is that Soap is sodium or potassium salt of fatty acid, whereas Detergent is sodium or potassium salt of sulphonic acid.

Soap vs. Detergent

A soap is a salt of fatty acids, whereas a detergent is a salt of sulphonic acid. A soap has – COONa group in it. Conversely, a detergent has –SO3Na group in it. Soaps do not work effectively with hard water, acidic water, and marine water. On the other hand, detergents work well with hard water, acidic water, and marine water.

Soaps are entirely biodegradable; they can be disintegrated by living organisms like bacteria. On the flip side, specific detergents consisting of branched hydrocarbon chains are non-biodegradable, which means they cannot be decomposed by living organisms.


Soaps do not work well with woolen garments, whereas a detergent can work its best with woolen garments. Soaps may cause irritation or itching to skin. Conversely, a detergent generally does not cause irritation or itching sensation to the skin. A soap dissolves slowly in water, whereas a detergent dissolves faster in water.

A soap is a chemical that is produced by a saponification reaction between fatty acid and a base like sodium hydroxide. On the flip side, a detergent is not made by a saponification reaction because it contains sulphonic acid instead of fatty acid. Soaps are comprised of natural ingredients, whereas a detergent has a synthetic origin.

The soap contains a straight-chain carbon skeleton with its one end having a carboxylic acid group. In contrast, a detergent contains a sulfate or sulphonate group instead of the carboxylic acid group at one end of its aliphatic or straight-chain carbon skeleton.


Comparison Chart

Sodium or potassium salts of fatty acid are called soaps.Sodium or potassium salts of sulphonic acid are called detergents.
Formation Reaction
Formed by the saponification reactionNot formed by the saponification reaction
Main Group
Carboxylic acid groupSulphonic acid group
Scum Formation
Forms scum with hard waterDoes not form scum with hard water
Lather Formation
Forms lather with hard waterDoes not form lather with hard water
Precipitate Formation
It forms a precipitate in hard water.It does not form precipitates in hard water.
Made Of
Natural ingredientsSynthetic sources
Fully biodegradableDetergents having branched hydrocarbon chain are non-biodegradable
Relation with Woolen Garments
Does not work wellworks well
Effects to Skin
Causes irritationDoes not cause irritation
Dissolution in Water
Effects on the Environment
Less harmfulMore harmful
Sodium stearate, sodium oleateSodium lauryl sulfate, sodium dodecylbenzene sulphonate

What is Soap?

A soap is a metal salt of fatty acid. A soap comprises an acyclic or straight-chain carbon skeleton with the carboxylic acid group at one end of the chain. Soaps are made by a saponification reaction between the carboxylic acid group and alkalies like sodium or potassium hydroxide. Calcium and magnesium hydroxide can also be used in the saponification reaction with fatty acid.

A soap is a surfactant that diminishes the surface pressure between a liquid and other substances and is used for cleaning our skin. Soaps are believed to be made of natural ingredients such as vegetal oils and animal fats. High-quality soaps are made up of oils like palm oil, castor oil, coconut oil, or olive oil by retaining them with natural glycerine.

Soap consists of the hydrophilic head in the form of a carboxyl group, whereas a hydrophobic tail in the form of a hydrocarbon tail. Soaps are environment friendly as they are biodegradable. They are decomposed easily by living organisms like bacteria and turn into simple compounds without causing pollution.

Soaps lean towards forming scum with hard water. Soap does not work well with hard water, acidic water, or marine water. Soaps tend to form lather with hard water. They may cause skin irritation.

Soaps have moderately weak purgative action as compared to detergents. Soaps work by acid-base reactions with dirt and grease molecules by turning them into fatty acids. Soap particles dissolve into ions. These ions surround the dirt particles, starting the cleansing action.

What is Detergent?

Detergents are generally of synthetic origin. Instead of a carboxylic acid group, detergents contain a highly ionic group of sulfate or sulphonate ion at one end of its aliphatic carbon skeleton. Detergents also include aromatic rings in them.

A detergent acts as a surfactant as well as a foaming agent. Detergent can also act as dispersants. Detergents also include nitrogen compounds in their formation, which appear as a ring in their structure. Conventional detergents use phosphate or sulfate head-groups, i.e., sodium dodecyl sulfate.

The effectiveness of detergents is not affected by the presence of certain minerals in water that is associated with hard water. Detergents can be defined as sodium or potassium salts of long-chain benzene sulphonic acid.

Detergents can be biodegradable or non-biodegradable. The detergents having a branched hydrocarbon chain are included in non-biodegradable detergents. Detergents can work well with hard water, saline water, or acidic water. They do not form scum and lather with hard water and have intense cleansing action as compared to soaps.

A detergent can be applied for cleaning woolen garments, while soap cannot be used for such purposes. Detergents dissolve faster in water as compared to soaps and do not irritate the skin. Detergents are not environment friendly as they release toxic chemicals in the environment and are non-biodegradable.

Detergents form thick foam that becomes a barrier for aquatic life respiration, resulting in the death of aquatic organisms. Detergents are categorized into three groups, including cationic detergents, anionic detergents, and zwitterionic detergents.

Key Differences

  1. A soap is sodium salt of long-chain carboxylic acid, whereas a detergent is sodium salt of long-chain benzene sulphonic acid.
  2. Soap has a carboxyl acid group at one end of its carbon skeleton. Conversely, a detergent has a sulphonic acid group at one end of its carbon skeleton.
  3. The hydrophilic head group of a soap molecule is a carboxylate anion. On the flip side, the hydrophilic head group for a detergent molecule is a phosphate or sulfate anion.
  4. The effectiveness of soap is greatly affected by the presence of mineral ions in water. On the contrary, the effectiveness of detergents is not affected by the presence of mineral ions in water.
  5. Soaps are considered to have weak cleansing action, whereas detergents have strong cleansing action.
  6. All the soaps are biodegradable and thus are considered environmentally friendly. On the flip side, detergents are mostly non-biodegradable and produce toxin materials; thus are not environmentally friendly.
  7. Soaps are not operative in hard water. Conversely, detergents are more effective in hard water.
  8. Soaps are not operational in saline water. On the flip side, detergents are more effective in saline or marine water.
  9. Soaps do not work well in an acidic environment, whereas detergents can work well in acidic as well as basic environments.
  10. Soap has a –COONa group in it. In contrast, a detergent comprises a –SO3Na group.


Soaps are metal salts of fatty acid, obtained from natural ingredients. On the other hand, detergents are metal salts of sulphonic acid, obtained from synthetic sources.

Harlon Moss

Harlon currently works as a quality moderator and content writer for Difference Wiki. He graduated from the University of California in 2010 with a degree in Computer Science. Follow him on Twitter @HarlonMoss