In rumors, it is believed that overnight Tea should not be consumed as drinking it can cause cancer. The reasoning behind this is the belief that overnight tea contains secondary amines which can transform into carcinogenic nitrosamines. In fact, this claim lacks scientific basis. Moreover, secondary amines themselves are not carcinogens; for nitrosamines to form, nitrate must be present and reach a certain quantity to have a carcinogenic effect.

From a hygiene perspective, tea left in an environment with poor sanitary conditions can easily breed spoilage microorganisms, causing the tea to turn sour and spoil. In such cases, the tea should not be consumed, as drinking it could lead to diarrhea or worse.

If stored in a clean and tidy environment, the tea is less likely to spoil. One can refer to the CCTV program “Is It True?” where they investigated the claim that overnight tea should not be consumed. Their conclusion was that overnight tea is safe and drinkable.

There is a significant component in tea called polyphenols, along with some vitamins, that inhibit the formation of nitrosamines. Polyphenols act as natural antioxidants. Comparing Taste and flavor, whether the tea has been left for 12 hours or 24 hours, as long as it hasn't gone bad, “even though it has been steeped for a longer time, it still retains the taste that the tea should have. For Pu'er tea, which emphasizes taste and smoothness, the overnight tea might even be better.”

Precautions: While “overnight tea” has many uses, during the summer when temperatures are high, tea can easily turn sour. If left for 24 hours, do not drink the overnight tea to avoid diarrhea.