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All About Soap

I recently started working at a company that makes natural bar soap. I've realized that even though bar soap is a common personal care product, most people do not know much about how it is made. Soap is unique from other beauty products for two main reasons: first, a chemical reaction occurs during the manufacturing process; and second, soap has a special regulatory classification in the United States.


Saponification is the process by which animal fats or vegetable oils are made into soap. A chemical reaction occurs when fatty acids are combined with a strong alkali base such as sodium hydroxide, also known as lye or caustic. The fatty acids react with the base to create an alkali salt and an alcohol. The alkali salt is the soap with cleansing properties and the alcohol is glycerol, also known as glycerin.

Common sources of fatty acids used in soapmaking include vegetable oils such as coconut, palm, canola, peanut, castor, olive, or jojoba and butters such as cocoa, shea, or mango. Animal fats can also be used such as beef tallow. You may remember the book and movie Fight Club in which human fat was used to make soap.

There are multiple methods to make soap, but all require saponification at some point in the process. The four main methods are cold process, hot process, melt and pour, and milling.

  1. Cold process is the simple combination of the fatty acid and alkali. For example, to make castile soap, olive oil and sodium hydroxide are combined to create sodium olivate and glycerin. Sodium olivate gives the cleansing properties to the final product.

  2. Hot process includes the same steps as cold process, but heat is added to accelerate the saponification process. Glycerin can also be removed from the final product when using a hot process.

  3. Melt and pour starts with a pre-made soap base which is then melted into liquid form, combined with any desired additives, and cooled back into solid form.

  4. Milling also uses a pre-made soap base that is physically shredded before being combined with any desired additives and pressed into solid form.


In a prior post on regulatory basics in the United States, I covered the differences between cosmetics and over-the-counter (OTC) drugs. As a refresher, the difference between cosmetics and OTC drugs is driven by the marketing claims made about the product as well as the formula ingredients and whether they are included in an OTC monograph. For soap, the differentiation is similar in that is it based on both the physical process by which the product is made and also the associated claims.

The law governing the regulatory classifications of cosmetics and OTC drugs is the Federal Food, Drug, and Cosmetic Act of 1938 which established the Food and Drug Administration (FDA) as a regulatory body. This law specifically excludes soap from the definition of a cosmetic product and therefore designates soap as outside the authority of the FDA:

The term "cosmetic" means (1) articles intended to be rubbed, poured, sprinkled, or sprayed on, introduced into, or otherwise applied to the human body or any part thereof for cleansing, beautifying, promoting attractiveness, or altering the appearance, and (2) articles intended for use as a component of any such articles; except that such term shall not include soap.

The FDA defines soap as a product which meets the following criteria:

Composition The product consists mainly of the alkali salts of fatty acids.

Cleaning The product's detergent properties are due to the alkali-fatty acid compounds and not any additional synthetic detergents.

Claims The product is labeled, sold, and represented solely as soap and is intended solely for cleansing the human body.

  • The product is regulated as a cosmetic if it is intended for purposes such as moisturizing the skin, imparting fragrance to the user, deodorizing the user’s body, or making the user more attractive.

  • The product is regulated as a drug if it is intended to cure, treat, or prevent disease, or to affect the structure or function of the human body. Examples include antibacterial cleansers that claim to kill germs, or cleansers that treat skin conditions, such as acne or eczema.

If the product meets these criteria, it is classified as soap and regulated by the Consumer Product Safety Commission instead of the FDA. If it does not meet the criteria, it is regulated as a cosmetic or drug product. To learn more, check out additional information from the FDA on regulatory classifications and FAQs.

I hope you found today's summary of soap interesting and informative. Do you have questions about the soap-making process? Are you surprised soap is categorized separately from other cosmetic products? Let me know in the comments section!

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