The use of American Chestnut (Castanea dentata) for treating poison ivy or oak exposure is justified primarily by traditional and historical accounts rather than robust scientific evidence. In North American folk medicine, especially among some Indigenous groups and early settlers, chestnut leaves and bark were sometimes used in poultices or washes for skin ailments, including rashes presumed to be from poison ivy. These uses were likely based on empirical observation and the astringent properties of tannins found in chestnut bark and leaves, which can help dry out weeping skin lesions and provide mild anti-inflammatory effects.

However, there have been no modern clinical trials or rigorous pharmacological studies validating the efficacy of American Chestnut for poison ivy or oak dermatitis. The existing evidence is anecdotal and based on ethnobotanical surveys or old herbal texts. While chestnut extracts do contain tannins and some antioxidant compounds, these are general properties shared with many other astringent plants, and not specifically targeted or proven against urushiol-induced contact dermatitis (the irritant in poison ivy/oak).

In summary, while American Chestnut's use for poison ivy or oak has some basis in traditional medicine, there is little to no high-quality scientific evidence supporting its effectiveness for this condition.