The extremely hard, gleaming auburn seeds of the Aesculus hippocastanum tree are called “conkers” in England. In North America, they are simply horse chestnuts. The buckeye-like seeds look edible, but they are considered toxic.

Native to western Asia, the horse chestnut tree was introduced to Europe in the 1500s and quickly became known as a healing plant for varicose veins, hemorrhoids, nerve pain and poor circulation. Today, standardized horse chestnut seed extract (HCSE) that focuses on the plant’s aescin content is well studied in Europe and used for treating vascular conditions, notably chronic venous insufficiency (CVI), varicose veins and hemorrhoids.

Given the seeds’ toxicity, cut horse chestnuts should only be used for external applications — unless under the care of a qualified practitioner. Topically, horse chestnut may be applied to unbroken skin as a poultice, lotion, gel or ointment to reduce swelling and minimize the appearance of spider veins and varicose veins.