The occasional sip of overnight tea does not produce any significant harm. Some people may have a misunderstanding or narrow understanding of the definition of overnight tea, calling tea that has been left overnight overnight tea. However, there is no fundamental difference between tea that has been set aside for a whole day and overnight tea, which is tea that has been placed for a long time. In the case that the tea is not contaminated, deteriorated, or well sealed, drinking tea that has been left for a long time usually does not have an obvious harmful effect on the human body. The concern about overnight tea is mainly due to the fear that nitrite will be produced in the tea, and a large amount of nitrite can produce carcinogenic substances under the action of digestion, so folklore rumors that drinking overnight tea has the danger of causing cancer. However, this claim has not been conclusively proven by clinical trials. Tea left overnight, or even longer, although it will increase the content of nitrite, but still within the safe dose, basically will not have a carcinogenic effect on humans. However, if the overnight tea is placed in a humid environment, and the tea is exposed to the air, it may breed bacteria, fungi, etc. Since the lights are dim at night and insects are active, bugs may accidentally enter the overnight tea, which may cause digestive symptoms such as vomiting, abdominal pain, diarrhea, etc. after drinking. In addition, some overnight tea is placed for a long time to precipitate, providing favorable conditions for the pigments in the tea to fully dissolve in the tea, and long-term, excessive consumption may cause the danger of yellowing teeth. In summary, although occasional consumption of overnight tea does not produce significant harm, it is still recommended to try to drink freshly brewed tea if possible.