If you sell soaps or if you simply wish your soaps to be properly labeled, you have a plethora of information sources available online. There's a problem, though...
Most of these sources, even some claiming to be "authoritative" are wrong in whole or in part.
Here's the real deal: How you must label your soaps depends on how you intend to sell your soaps.
There are three federal government agencies which may regulate your product labeling: The Food and Drug Administration (FDA), the Consumer Product Safety Commission (CPSC) and the Federal Trade Commission's Bureau of Consumer Protection (BCP).
The FDA regulates drugs, cosmetics and tobacco products to protect the public from ingestion or contact with harmful substances.
The CPSC regulates consumer products to protect the public from issues of potentially hazerdous ingredients, design or uses..
The BCP is tasked with avoiding misleading labeling practices for consumer goods aas per the federal Fair Packaging and Labeling Act (FPLA).
If you present your product as a "soap" and no more, your product is NOT regulated by the FDA at all. It is, however, subject to the FPLA and review and potential regulation by the CPSC if any product safety issues are identified.
For instance, if you claim your product has health or cosmetic benefits such as deodorizing, moisturizing or imparts a fragrance to the skin after use, it is legally regulated by the FDA even though it may otherwise be a pure soap substance. If any claims are made as to defoliating, skin smoothing, alleviating or curing any illness or medical condition, it is also regulated by the FDA.
Soap has a singular status in government product regulations. Traditionally, any product that derives its cleansing effect solely from and is composed primarily of saponified fatty acid substances, and is only presented, labeled and sold as "soap" is specifically NOT itself a regulated product per Federal law. This goes way back in American history.
The modern reality, however, is that this exemption exists in a narrowly defined manner. Further, with the establishment of the CPSC and the FPLA, soap products or packaging may be subject to review and potential relevant regulation to protect public safety as any other kind of product may be.
Your soap products are also subject to other general product labeling requirements as may exist under other federal laws or in each state, regardless of it being a pure "soap" as per the FDA's rules. For instance, under the federal Fair Packaging and Labeling Act, product net weight or item count must be clearly displayed (in US and metric measures) on the front of the product packaging and the product manufacturer's name and address and contact information is required on the label (Manufacturer's website suffices if that website provides consumer contact information*). Check your state laws for clarification of any state regulations that may also apply (Minimum font sizes may be regulated, etc).
* "The statement of the place of business shall include the street address, city, state, and zip code; however, the street address may be omitted if it is listed in a readily accessible, widely published, and publicly available resource, including but not limited to a printed directory, electronic database, or Web"
The bottom line is this:
If your product is formulated, packed and presented as only a "soap" as per the narrow FDA definition, you are NOT required to list any ingredient information on your labels other than "soap". If you choose to do so, you are NOT required to list ingredients in any specified manner as there is no applicable law requiring such for a defined "soap" product. Specifying product contents as only "soap" is quite acceptable. You ARE generally required by regulations to identify the manufacturer and the manufacturer's address or contact information in a legible font size and manner. Manufacturer's website is acceptable if that website provides information or means to contact the manufacturer. If you produce in large quantities, best practices should include a traceable product manufacturing batch number or other traceable indicator should any product recall be necessary. "Common sense" applies here. Periodically review the current notices from the CPSC on their website (below) for relevant issues or directives as may pop up so as to keep current with any potential future requirements from the CPSC.
If your product does NOT conform fully with the narrow FDA definition of a "soap", your body care product is subject to the FDA's full regulation as per the FD&C Act *as a "drug" or as a "cosmetic". I refer you to the FDA and FD&C websites for complete definitions and applicable regulations to your particular products. FDA and FD&C specific regulations RULE here. "Common sense" is secondary - FOLLOW the rules as published, NOT anyone else's summary of their opinions (including mine). The FDA has enormous clout - You do NOT want to violate their rules.
* The United States Federal Food, Drug, and Cosmetic Act (abbreviated as FFDCA, FDCA, or FD&C), is a set of laws passed by Congress in 1938 giving authority to the U.S. Food and Drug Administration (FDA) to oversee the safety of food, drugs, and cosmetics.
Is It a Cosmetic, a Drug, or Both? (Or Is It Soap?)