When using a mouthwash, do you gargle for a few quick seconds before spitting? Most mouthwashes work best when in oral contact for 30 seconds per use. However, some mouthwash may cause burning sensation and is not suitable to be use for that long. Hence, it is wise to use a mouthwash that is free of alcohol and fluoride to avoid burning sensation and discoloration of enamel that can lead to damaged teeth after prolonged use.