The horse chestnut tree is native to Asia and northern Greece, but it is now cultivated in many areas of Europe and North America. The tree produces fruits that are made up of a spiny capsule containing one to three large seeds, known as horse chestnuts. Modern extracts of horse chestnut are usually made from the seeds, which are high in the active constituent aescin (also known as escin).

Horse chestnut leaves have been used by herbalists as a cough remedy and to reduce fevers. The leaves were also believed to reduce pain and inflammation of arthritis and rheumatism. In traditional herbal medicine, poultices of the seeds have been used topically to treat skin ulcers and skin cancer. Other uses include the internal and external application for problems of venous circulation, including varicose veins and hemorrhoids.

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.

Studies and 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.

For treatment of chronic venous insufficiency, horse chestnut seed extracts standardized for aescin content (16–20%), 300mg are used 2 - 3 times per day. Tincture, 1 - 4ml taken three times per day, can be used though it is questionable whether a significant amount of aescin can be absorbed this way. Gels or creams containing 2% aescin can be applied topically 3 - 4 times per day for hemorrhoids, skin ulcers, varicose veins, sports injuries, and trauma of other kinds.