Sugars contain a high amount of fermentable carbohydrates which become the source of nutrition for the oral bacteria and the reason for plaque formation on the surface of the tooth. These bacteria ferment the carbohydrates to produce acids that cause acid erosion of the enamel.
Desensitizing mouthwash contains the mild anesthetic agent to numb the nerves endings present in the center of the tooth. Also, it has desensitizing agents that form crystals which clog the dentinal tubules. Blocked dentinal tubules cannot transmit pain sensation to nerves and relieve tooth sensitivity.
If you have one sensitive tooth, then you should book an appointment with your dentist. There can be many reasons for a single tooth to be sensitive such as tooth decay, cracked tooth, loose filling, etc.