Bath fizzies are infeasible as liquids because of the inability to keep the mixture from reacting prematurely. This is a distinction from foam bath (see below) preparations, which may be supplied as liquids or solids.
When the term "bubble bath" is encountered on the Internet referring to a gas-infused bath or pool, it is more often by a non-native user of English who may not be aware of its use to refer to foam baths (see below). In other languages the distinction is more likely to be kept by use of different words.
Bubbles on top of the water, less ambiguously known as a foam bath (see photo), can be obtained by adding a product containing foaming surfactants to water and temporarily aerating it by agitation (often merely by the fall of water from a faucet). The practice is popular for personal bathing because the foam insulates the bath water, keeping it warm for longer, and (as a lime soap dispersant) prevents or reduces deposits on the bath tub at and below the water level (called "bathtub ring" and soap scum, respectively) produced by soap and hard water. It can hide the body of the bather, preserving modesty or, in theatre and film, giving the appearance that a performer who is actually clothed is bathing normally. Children find foam baths particularly amusing, so they are an inducement to get them into the bathtub.
Surfactant preparations for this purpose are themselves called "bath foam", "foaming bath", or "bubble bath", and frequently contain ingredients for additional purposes common to bath additives. Used at much higher concentration (for instance on a washcloth), such preparations (especially in liquid form) may also be used to wash skin or hair, so they are sometimes marketed for combined purposes; in a few cases, mild household detergents for hand washing of articles have also been labeled for such purposes, or for preventing soap scum on the bathtub (with or without foaming).
Effervescent bath products came into use as effervescent bath salts early in the 20th Century; the bath bomb became a popular form late in that century. The earliest foam baths were foamed with soap, which practice came about shortly after soap flakes were marketed. Saponins were also used to foam machine-aerated baths. Foam baths became more popular with later surfactants; an early publicized use of an alkyl sulfate surfactant as bath foam was in the original 1936 production of the play The Women, but it is possible that a similar composition was used to produce foams seen in bath photos since the marketing of Dreft in 1933. Foam baths became standard practice for bathing children after the mass marketing of products so positioned in supermarkets during the 1960s and thereabouts, Bub in the United States and Matey in the United Kingdom having been marketed shortly before 1960; the dubious claim had been made that their normal use (diluted in a tubful of water) would substitute for soap and/or rubbing to clean skin.
Machine-aerated baths originated in the early 20th Century for therapeutic use, becoming more widely used with the introduction of the Jacuzzi. Trends merged when the hot tub, which originally had still water, with its increasing popularity became more commonly a communal whirlpool bath. By the late 20th Century jetted bathtubs had become popular for home installation.
It is possible to produce baths with bubbles simultaneously in and on top of the water (as in a poured beer), but the combination has not been popular. Mechanical aeration of a foam bath may produce much more foam than is sought -- the Internet is replete with first hand accounts and sometimes photographs of such experiences -- and many mechanically aerated baths are hot tubs which are shared and not drained between uses and so are desired to be kept free of non-maintenance materials. Mechanically aerated baths for tissue debridement of burn victims typically have added anti-foaming agents to counteract the film-forming properties that some medicinal additives have as a side effect, but the anti-foam is sometimes omitted or reduced for children to give them more of a pleasant distraction during debridement. Bath fizzies that also foam tend to produce disappointingly little foam when allowed to do so from their own fizz, and aeration of the water loses the gas from the fizz.