The seeds are the source of a saponin known as aescin, which has been shown to promote circulation through the veins. Aescin fosters normal tone in the walls of the veins, thereby promoting return of blood to the heart. This has made both topical and internal horse chestnut extracts popular in Europe for the treatment of chronic venous insufficiency and, to a lesser extent, varicose veins. Aescin also possesses anti-inflammatory properties and has been shown to reduce edema (swelling with fluid) following trauma, particularly following sports injury, surgery, and head injury. A topical aescin preparation is very popular in Europe for the treatment of acute sprains during sporting events. Horse chestnuts also contain flavonoids, sterols, and tannins.
Double-blind and preliminary clinical trials have shown that oral horse chestnut extracts reduce the symptoms of chronic venous insufficiency, including swelling and pain. Those suffering edema after surgery have also found relief from topical application of horse chestnut extracts, according to preliminary studies.