Common use involves rinsing the mouth with about 20ml (2/3 fl oz) of mouthwash. The wash is typically swished or gargled for about half a minute and then spit out. Most companies suggest not drinking water immediately after using mouthwash. In some brands, the expectorate is stained, so that one can see the bacteria and debris.^[5][6] Mouthwash should not be used immediately after brushing the teeth so as not to wash away the beneficial fluoride residue left from the toothpaste. Similarly, the mouth should not be rinsed out with water after brushing. Patients were told to "spit don't rinse" after toothbrushing as part of an National Health Service campaign in the UK.^[7]

Gargling is where the head is tilted back, allowing the mouthwash to sit in the back of the mouth while exhaling, causing the liquid to bubble. Gargling is practiced in Japan for perceived prevention of viral infection. One commonly used way is with infusions or tea. In some cultures, gargling is usually done in private, typically in a bathroom at a sink so the liquid can be rinsed away.^{[citation needed]}

The most common use of mouthwash is commercial antiseptics, which are used at home as part of an oral hygiene routine. Some manufacturers of mouthwash state that antiseptic and anti-plaque mouth rinse kill the bacterial plaque that causes cavities, gingivitis, and bad breath. Anti-cavity mouth rinse uses fluoride to protect against tooth decay. It is, however, generally agreed that the use of mouthwash does not eliminate the need for both brushing and flossing.^[8][9][10] The American Dental Association asserts that regular brushing and proper flossing are enough in most cases, although they approve many mouthwashes that do not contain ethanol (in addition to regular dental check-ups).^[11] For many patients, however, the mechanical methods could be tedious and time-consuming and additionally some local conditions may render them especially difficult. Chemotherapeutic agents, including mouthrinses, could have a key role as adjuncts to daily home care, preventing and controlling supragingival plaque, gingivitis and oral malodor.^[12] Another common use of mouthwash is prior to and after oral surgery procedures such as tooth extraction.

Minor and transient side effects of commercial mouthwashes are very common, such as taste disturbance, tooth staining, sensation of a dry mouth, etc. Alcohol-containing mouthwashes may make dry mouth and halitosis worse since it dries out the mouth.^[13][14] Soreness, ulceration and redness may sometimes occur (e.g. aphthous stomatitis, allergic contact stomatitis) if the person is allergic or sensitive to mouthwash ingredients such as preservatives, coloring, flavors and fragrances. Such effects might be reduced or eliminated by diluting the mouthwash with water, using a different mouthwash (e.g. salt water), or foregoing mouthwash entirely.