Horse chestnuts shouldn't be eaten. Raw horse chestnuts contain a poison called esculin. Esculin is especially abundant when the horse chestnut seed is young. Ingesting this poison can make a person violently ill, and it can be fatal.
When prepared correctly, horse chestnut seeds can be used medicinally. They are used to treat fever, diarrhea, hemorrhoids, phlebitis, varicose veins and other problems with the veins and circulatory system.
The horse chestnut is an ornamental tree with white flowers that bloom in the spring. Later, the tree produces green capsules that hold the horse chestnuts, or conkers. Despite its name, the horse chestnut is only distantly related to the common chestnut.