Tannins are very astringent chemicals found in a number of plants. One of them is the tannic acid, which doesn't have a strong chemical reactive power. It is believed that some trees produce tannic acid because it is not flammable and its unpleasant taste repels insects and animals. However, tannins have antioxidant effects and can kill bacteria and fungus, so they are useful in human medicine. Tannins are also used in industry, in particular in the processing of wood and leather.
Numerous plants and trees have a content of tannins but one of the richest sources is the banana tree (scientific name Musaceas Musa). Tannic acid is also easily extracted from oak species from the Quercus family, especially the Quercus infectoria. The highest concentration is in the nutgalls of these oaks.
Tannic acid has a disgusting taste and can make people puke if they consume it. Otherwise, it doesn't normally smell at all and looks like a soluble powder that can range in color from white or yellow to brown. While tannic acid provides a number of health benefits, it also has serious side effects on humans. It should not be ingested in large doses or taken on a regular basis in order to prevent such problems.
The main reason why tannic acid can be harmful is that it limits the intake of iron in the body. This can have very bad consequences, since iron is an essential mineral that plays many roles and is the building block of red blood cells. Tannic acid also appears to cause serious damage to the kidneys and liver and can cause digestive issues as well.
However, tannic acid is not dangerous if consumed with caution, in normal doses. Most of the negative effects are caused by overdoses or by ingesting the compound in pure form. It is not a good idea to take tannic acid without medical advice. The compound is otherwise harmless, it has been present in human diet for a long time without any side effects, especially in wine kept in oak barrels, which absorbs some of the tannic acid from the wood.
Some trees like the oaks or sequoia have a natural content of tannic acid in their wood. It is used in industry to change the color of other wood varieties. Probably the oldest human usage of tannic acid was in leather manufacturing. The tannic acid tans animal hides when applied on them and turns them into leather, a very useful property for the early humans.
One of the side effects of tannic acid on humans is that it can lead to constipation, which is actually very useful in the treatment of diarrhea. For the same reason, it helps against internal bleeding and can limit the inflammation caused by hemorrhoids. Tannic acid kills fungus and can be applied externally on feet and nails in order to eliminate it. It is a general purpose ingredient in creams for external use, since it speeds up the healing of wounds and can treat muscular or articular issues.
Tannic acid is effective against poison and was one of the three ingredients in the so-called universal antidote against poison, which also included magnesium and activated charcoal. While the combination was reasonably effective, it was not known at the time that the charcoal absorbed the tannic acid, pretty much neutralizing both of them. Ironically, the three compounds were probably better against poison when used separately, while the combination was weaker.
Even today, tannic acid remains a useful external cure for stopping bleeding and in the treatment of a variety of skin problems. The tannic acid can be put directly on an area affected by diaper rash, prickly heat, poison ivy irritation, fever blisters, cold sores, ingrown toenails, sore tonsils, sore throats, rashes or receding gums.
The compound can also be taken orally for the treatment of various diseases. These include dysentery, bloody urine, chronic diarrhea, internal bleeding, some forms of cancer, inflamed joints and chronic cough. It can also be used as a vaginal douche in order to clear leucorrhea, which is unpleasant white or yellow discharge.
Its ability to treat skin problems has been known for a long time and it is still used as such. Modern scientists also suspect that tannic acid could limit the expansion of cancer, but this is not confirmed by studies yet.
Tannic acid also has a number of industrial uses. It is added for flavour in the food industry. It remains an important ingredient in leather and wood processing, as well as the production of ink. It limits the effect of hemorrhoids and is added to suppositories made for this purpose.
Tannic acid doesn't cause any problems when found in food or wine but it seems that some of its traditional medical uses are dangerous. It's not recommended to apply it externally on the skin to treat burns or rashes (as described above). The American FDA (Food and Drug Administration) also warns against applying it on the lips against sores or various blisters. In all these situations, the problem is that the tannic acid is easily absorbed into the body and can lead to an overdose. However, these are just precautions, since no serious study has confirmed these issues so far.
It is known that tannic acid in high doses has both minor and serious side effects. It can cause nausea but also irritates the stomach, leading to vomiting, or even hurting the liver. It also appears to cause cancer in high concentrations, since people who constantly eat plants with a high tannic acid content can get throat or nasal tumours.
Like most compounds, tannic acid must be avoided during pregnancy and nursing. It is especially hazardous to use it on wounds or large areas of skin. No real tests have been made to show its effects on pregnant or lactating women, who should avoid it to be safe.
Tannic acid can hurt the kidneys and people who already have such problems will get even more damage. As a result, it shouldn't be used at all by people with kidney diseases. It also damages the liver and must be avoided by people who suffer from related issues.