My wife recently spotted the following perplexing line on Crabtree & Evelyn's website, advertising their hand soap:

Our gentle cleansing liquid soaps are pH-balanced and soap-free.

That's right, they're selling soap-free soap. I've heard of a "nothing-burger," but "nothing-soap"?

It's not just Crabtree & Evelyn, either: Healthy Oil Planet advises that "some of the best tea tree soaps are soap-free cleansers." And a distributor by the name of Shaklee has a whole variety of "soap-free soaps" for sale.

Intrigued by this seeming paradox, I did a little hunting around to try to figure out when soap is not, in point of fact, soap. First, let's look at the Visual Thesaurus definition of the word: "a cleansing agent made from the salts of vegetable or animal fats." That's pretty broad, but others define soap more narrowly. In the U.S., the Food and Drug Administration takes a hard line on what counts as soap. Here's what the FDA website has to say:

Not every product marketed as soap meets FDA's definition of the term. FDA interprets the term "soap" to apply only when —

  • The bulk of the nonvolatile matter in the product consists of an alkali salt of fatty acids and the product's detergent properties are due to the alkali-fatty acid compounds, and
  • The product is labeled, sold, and represented solely as soap.

If you care about the nitty-gritty of the first point, check out the Wikipedia page on soap, which provides loving detail about how fatty acids are treated with strong alkaline solutions (typically lye) to produce an "anionic surfactant." The whole process is known as saponification.

So what happens if this strict definition of soap is not met — say, if a cleanser or detergent is created by a process not involving lye? The FDA warns that "if a product intended to cleanse the human body does not meet all the criteria for soap, as listed above, it is either a cosmetic or a drug." This is a crucial point for manufacturers who might be subject to entirely different regulations for cosmetics or drugs.

After delineating when these not-quite-soapy cleansers are regulated as cosmetics and when they're regulated as drugs, the FDA adds a final rule:

If a product —

  • is intended solely for cleansing the human body and
  • has the characteristics consumers generally associate with soap,
  • does not consist primarily of alkali salts of fatty acids,

it may be identified in labeling as soap, but it is regulated as a cosmetic.

So even if Crabtree & Evelyn's products are "soap-free" according to the narrow sense of soap, they can still be identified by that term if they have "the characteristics consumers generally associate with soap." Producers of these cleansers want to use easy-to-recognize labels like "hand soap," but at the same time they want to tout the stuff as "soap-free" to indicate its gentleness to the skin. The FDA doesn't seem to mind this self-contradictory marketing strategy.

This paradox isn't actually so paradoxical if you look at the word soap as filling what semanticists call "marked" and "unmarked" categories. The unmarked category is the more general one, while the marked one is more restricted. Some words can be either marked or unmarked, depending on the context. For instance, the word cow can refer to cattle in general, but it can also refer to the female only (as opposed to bull). Similarly, finger can refer to any digit of the hand, or it can have a more restricted sense excluding the thumb. Thus a cleansing product can simultaneously be soap (in the unmarked sense) and free of soap (in the marked sense).

By the way, if the title of this column is opaque, it's an allusion to an old joke, or rather an anti-joke. "No soap, radio" is a classic example of "anti-humor" where the joke is that there's really not a joke. (Wikipedia has more, as does a thorough survey by Chris Hays of Stanford University.) It might seem odd, but a joke with no joke is no weirder than a soap with no soap.