Tannic acid is a type of tannin, a natural chemical called a polyphenol found plants. Tannins are naturally bitter with astringent properties that protect them against insects and destruction by wildfires. These natural polyphenols are found in the seeds, roots, stems, leaves and buds of a number of plants. Some of the best food sources of tannins are tea, wine, fruit juice and fruit. Nuts, legumes, chocolate and some herbs also contain tannins.
Tannin and tannic acid are terms that are often used interchangeably, but they aren't the same. Tannic acid is a commercial form of tannin made up of a mixture of plant-based compounds. It was developed as a stain for wood and leather but has other applications as well. It's used as a mordant for dyeing cotton and wool and for making ink. It consists of a dark yellow powder that readily dissolves in water.
Food-grade tannic acid is used as an additive in some commercial food products. As a food additive, it functions as an emulsifier and stabilizer to keep oil and water-based ingredients from separating from each other. It also thickens and adds color and flavor to food products and is a common ingredient in soft drinks, juice and wine. Contrary to popular belief, tea contains tannins but not tannic acid. Some foods that contain tannins or tannic acid can trigger migraine headaches in some people.
Tannic acid has been used medicinally for hundreds of years to treat certain types of poisoning, including strychnine poisoning. Around the time of the World War I, it was used to treat burns. It's not used for that purpose today but is still used pharmaceutically as a treatment for diarrhea and to produce some medications. Some people use it to soothe minor skin irritations like diaper rash and heat rash and to treat cold sores, fever blisters, skin rashes and sore throats. Tannic acid has an astringent effect that helps to shrink swollen tissues. This makes it an effective treatment for hemorrhoids. Creams and sitz baths to treat hemorrhoids commonly contain tannic acid. As an astringent, tannic acid also reduces under-eye swelling and puffiness. That's why it's popular to use hemorrhoid treatment creams to reduce eye puffiness.
Due to its astringent properties, tannic acid is an ingredient in some cosmetic and skin care products, most commonly astringents and toners. Astringents cause tissues to constrict. This helps to tighten pores and make them look less obvious. They also help to remove dead skin cells and residual sebum and make-up that can make skin look dull. Tannic acid is also an ingredient in face creams and moisturizers formulated to firm skin and make it look more youthful due to its skin tightening effect. Other cosmetic and personal care products that may contain tannic acid are sunless tanning lotions, oral gels used to treat mouth pain and wound treatment products.
According to a study published in the Journal of Investigative Dermatology, tannic acid may be beneficial for treating atopic dermatitis, an inflammatory skin condition triggered by certain foods and environmental factors. Tannins and tannic acid have natural anti-inflammatory properties that may explain their benefit for treating this condition.
Is it safe? Eating foods and drinking beverages that contain large amounts of tannic acid or tannin can cause stomach upset. Tannins also reduce the absorption of some nutrients from the intestinal tract, particularly iron. At high doses in animals, they can cause liver damage, kidney problems and respiratory failure, although this is at doses far greater than people typically consume. More commonly, foods that contain tannins or tannic acid cause mild stomach irritation. Some research suggests that consuming foods high in tannic acid may increase the risk of nose, throat or esophageal cancer, while other studies show that tannins and tannic acid are protective against certain types of cancer.
In quantities found in cosmetic and skin care products, tannic acid appears to be safe. The Environmental Working Group's Skin Deep Cosmetics Database classifies it as a low hazard cosmetic ingredient. It can cause skin and eye irritation and shouldn't be used too close to the eyes.