A bubble bath is a filled bathtub with a layer of surfactant foam on the surface of the water and consequently also the surfactant product used to produce the foam or soap. Less commonly, aerated or carbonated baths are called bubble baths.
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 filling the tub). The practice is popular for personal bathing because of the belief that it cleanses the skin, that 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 often find bubble baths enjoyable, so they are an enticement 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 enhancers. Used at much higher concentration (for instance on a washcloth), such preparations (especially in liquid format) 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).
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