Netizen Inquiry: I saw an article online saying that drinking overnight tea can cause cancer and other health hazards like diarrhea. Is this true?
Chang-Hsing Reply: This is an internet rumor that has been circulating for a long time, and there is no evidence to support that drinking overnight tea causes cancer. However, if tea leaves are steeped for too long, they can spoil and breed bacteria, which may pose health risks. If you smell that the tea liquor has turned sour or cloudy, it is best to pour it out and not drink it, regardless of whether it is overnight tea or not.
Aside from spoilage and bacterial growth, if tea leaves are steeped for too long, tannins and caffeine continue to be released, making the tea liquor bitter and astringent. Excessive tannins and caffeine can easily cause stomach discomfort and heart palpitations, which are also common drawbacks of overnight tea.
There is no evidence to prove that drinking overnight tea causes cancer; at worst, it might upset your stomach. Even so, we still recommend not steeping tea leaves for too long. Remove the leaves within one hour after hot water steeping. If the tea liquor cannot be finished on the same day, it is best to refrigerate it.