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Acids Present in Soap

Fatty acids are an inseparable ingredient in soaps. The type of acid used in a soap mainly determine the properties of that soap. Let's see the different acids that are present in soap.
Ashwini Kulkarni Sule Nov 5, 2018
The art of soap making dates back several centuries. Ancient people supposedly used soap-like materials for cleaning. Soap is a combination of oils or fatty acids and alkali. The resultant reaction produces glycerin and sodium salt due to the fatty acid used. Different combination of fatty acids and alkali are responsible for the various properties of soap.
Lather, cleansing ability, and the mode of reaction of the soap are all dependent on the particular acid in the soap. If you are interested in making soap, you may go through the list of some commonly used fatty acids.

Fatty Acids Present in Soap

As mentioned earlier, the fatty acid content in the ingredients will determine the eventual characteristics of your finished product, i.e. soap. Let us take a look at some of the fatty acids involved in making soap and the characteristics that each of them lend to the soap.

Stearic Acid

Stearic acid is the most important ingredient for making soap bars. It renders hardness to the soap mixture, which facilitates its molding. It also gives a creamy texture to the soap lather. Stearic acid also has strong cleansing properties. Overusing stearic acid in bath soaps results in dryness of skin.

Lauric Acid

Lauric acid is also responsible for the hardness of soap. It produces rich, fluffy lather. It has immense cleaning abilities which help to get rid of oil, grease, etc. If used in large amounts in bath soaps, it can strip the skin of its moisture and natural oils. Ingredients like coconut oil, Babassu oil, or palm oil are rich sources of lauric acid.

Oleic Acid

Oleic acid is responsible for the slippery, soapy feel of the soap bar. Oleic acid is a good skin conditioner which is used in bath soaps for its moisturizing properties. However, oleic acid does not produce a rich lather.

Linoleic Acid

Linoleic acid also has good moisturizing properties. The silky, smooth feeling that you experience after having a bath with certain soaps is due to the linoleic acid present in them. It has the property to turn rancid more quickly than other acids. 
This often leads to formation of orange spots on the soap bar. Thus, linoleic acid is to be avoided if you want your soap bar to last long. Linolenic acid is also known for its moisturizing and nourishing properties. It is used for very mild soap formulations.

Linolenic Acid

Linolenic acid is also known for its moisturizing and nourishing properties. It is used for creating very mild finished product of soap.

Ricinoleic Acid

Ricinoleic acid is mainly used in making soap for its ability to produce very dense, rich lather. It can produce foamy as well as creamy, stable lather. Even small amount of ricinoleic acid is capable of producing thick lather.

Palmitic Acid

The properties of palmitic acid are somewhat similar to those of stearic acid. Thus, palmitic acid and stearic acid are interchangeable in preparation of soap.

Myristic Acid

Myristic acid has all the properties of making a good soap. It has powerful cleansing ability and produces a luxurious amount of fluffy lather. However, if you go overboard with using myristic acid, it could lead to drying up of the product.
Besides the listed fatty acids, there are several other forms of acids which are used in soaps.
  • Salicylic acid is a commonly used acid in soaps and other cosmetics for its acne fighting properties. It has good exfoliating properties which are effective against acne.
  • Kojic acid is used for lightening the skin. Regular use of kojic acid soap is known to reduce pigmentation; however, one must not discontinue the use of this soap.
  • Etidronic acid is used to counter the undesirable effects of metal ions in certain soap ingredients. It is also used as a binding agent in several other cosmetic products.
The type of acid in soap is basically dependent upon the specific use of the soap. The proportions and ratio of the listed acids also vary according to the type and purpose of the soap.