Can brewing tea with a thermos cup cause cancer?

Some people use insulated cups to make tea, so that they can drink hot tea at any time, but others say that using insulated cups to make tea is not healthy and can easily lead to poisoning. The reason for this statement is that using insulated cups to brew tea can easily produce tea stains. Therefore, some people are concerned that tea stains will stick to the inner wall of insulated cups for a long time and corrode stainless steel, leading to the dissolution of heavy metals.
In fact, although tea itself has a weak acidity and alkalinity, for stainless steel insulated cups that meet the standards, there is no need to worry about alloy elements leaching out when used for brewing tea, because the chromium element contained in stainless steel can ensure the formation of a passivation film on the stainless steel surface, which can protect the stainless steel substrate.
Even if trace amounts of alloy elements corrode and dissolve, the chromium, nickel, manganese, molybdenum and other alloy elements in stainless steel for tableware are essential trace elements for our human body and will not affect our health.
Although using a thermos cup to make tea will not cause poisoning or cancer, it is not recommended to use it for brewing because soaking tea leaves in high temperatures for a long time can affect their taste and nutrition, allowing the tea polyphenols in the tea to be fully dissolved, and the aromatic and active substances in the tea to be destroyed by heat, resulting in a thick and dark color of the tea soup, making it even more bitter to drink.
In addition, milk soybean milk is also not recommended to be put into a warming cup, because both milk and soybean milk are high protein foods, and long time storage at the appropriate temperature is likely to cause a large number of bacteria to multiply, while milk soybean milk, once breeding bacteria, will quickly deteriorate, rancidity, look like a bean curd jelly served with sauce like flocculent, and easy to cause diarrhea after eating.
As a daily item, for the sake of health, when choosing insulation cups, we must pay attention to selecting stainless steel insulation cups that meet quality standards.