"Bath salts" are one of a multitude of marketing gimmicks under which psychoactive research chemicals, typically stimulants, are frequently sold. Chemicals sold under this pretext have no legitimate value as bath salts.
Psychoactive research chemicals occupy a legal grey area in most jurisdictions. Although often not explicitly controlled substances, distribution with intent for human consumption may violate various laws and statutes. In the United States for example, distribution of many research chemicals would contravene the Federal Analog Act if there is demonstrable intent for human consumption. In other nations laws regarding public safety and pharmaceutical licensing may be breached if unregulated and unapproved chemicals are sold for consumption.
In an attempt to minimize the risk of legal action research chemicals are therefore typically labelled as 'not for human consumption'. Some distributors take this a step further by proposing spurious applications for which these chemicals might be used. This extends the facade that a distributor is unaware that a product may be intended for human consumption.
The most common examples of such gimmicks are "plant food" and "bath salts", both of which have been typically used to market beta-ketone stimulant research chemicals (though there is no reason that other chemicals could not be sold under a similar gimmick). Despite these marketing claims there is no supportive evidence that the products are fit for the proposed purpose. Many of the chemicals sold under this gimmick may actually be irritants to the skin and eyes, making them totally unsuitable for use as an actual bath salt. They are also not a nutritionally balanced supplement for plants.