With its many applications in food, as medication, and in manufacturing, one can assume it is safe, correct? Not at all.
Tannic acid seems UNSAFE when applied to the skin to treat diaper rash, prickly heat, and minor burn or sunburn. The US Food and Drug Administration (FDA) is worried that tannic acid might also be unsafe when used to treat cold sores and fever blisters on the lips. The concern is that the tannic acid might be easily absorbed through the lips and cause harmful side effects. But there isn’t enough research yet to know for sure. The FDA has asked for more studies. No studies prove this to be true or false at the moment.
In large amounts, tannic acid can cause side effects such as stomach irritation, nausea, vomiting, and liver damage. Regular consumption of herbs with high tannin concentrations seems to be associated with an increased chance of developing nose or throat cancer.
Special Precautions & Warnings:
Pregnancy and breast-feeding: It’s UNSAFE to apply tannic acid to broken skin or large areas of skin. There is concern that it might be absorbed and cause harmful side effects.
The safety of taking tannic acid by mouth during pregnancy and breast-feeding is unknown. Stay on the safe side and avoid use.
Kidney problems: Tannic acid can cause kidney damage, making existing kidney problems worse. Don’t use tannic acid if you have a kidney disorder.
Liver problems: Tannic acid can cause liver damage, making existing liver problems worse. Don’t use tannic acid if you have a liver disorder.