Traditional concepts, people usually think that overnight tea can not drink. Because the tea is placed for too long, not only the taste becomes bitter, and some nutrients such as tea polyphenols, vitamin C will be further oxidized, weakening its health effects. In addition, due to the long time, coupled with high temperature, a large number of proteins in the tea leaves are prone to corruption of bacteria, microorganisms and rancidity, leading to diarrhea. There is also a theory that tea put overnight, will produce nitrosamines this carcinogen, drink overnight tea will get cancer.

But on the other hand, there is no definitive research evidence to support what happens when people drink overnight tea. Tea left for a long time will change from turquoise to reddish-brown, which is due to the oxidation of tea polyphenols into reddish-brown tea pigments, these products are said to be non-toxic, will not be harmful to the human body. Some people say that overnight tea is carcinogenic, some people say it is not carcinogenic, the view of carcinogenicity is the conclusion of laboratory animal testing, the view of non-carcinogenicity is a kind of extrapolation - overnight tea in the nitrosamines are insignificant, will not bring cancer hazards to the human body. "However, generally substances with hidden toxicity are not immediately effective, and the effect occurs only when they are consumed over a long period of time, chronically and in large quantities, so why would we want to experiment with our own bodies?"

So, although overnight tea is not absolutely harmful, but still drink less for the better, especially the deterioration of overnight tea can not drink. Drinking tea is still appropriate to drink with the bubble, not only pure taste, but also to reduce pollution.