Tannins have a long history of traditional use for treating external bleeding, especially in herbal and folk medicine systems worldwide. Tannins are polyphenolic compounds found in many plants, including oak bark, witch hazel, tea, and certain medicinal herbs. Their astringent properties cause the contraction of body tissues and blood vessels, which can help reduce bleeding and promote clotting when applied topically to minor wounds and abrasions. Historical texts and ethnobotanical records frequently mention the use of tannin-rich plant extracts or poultices to stop bleeding and accelerate wound healing.

From a scientific perspective, there is a plausible mechanism for these effects: tannins can precipitate proteins on the surface of wounds, forming a protective barrier and aiding hemostasis. Some laboratory and animal studies have demonstrated the hemostatic and antimicrobial activities of tannin-containing extracts. However, robust clinical trials in humans are lacking, so current support comes mostly from traditional use and limited preclinical data.

In summary, while the traditional use of tannins for external bleeding is well documented and supported by some scientific rationale, high-quality evidence from clinical studies is insufficient. Therefore, the use of tannins for this purpose is justified primarily by tradition, with moderate supporting evidence.