(Equisetum arvense) The medicinal use of horsetail dates back to ancient Greece and Rome. Because of its high silica content, horsetail can be essential in treating hair loss. No other herb in the entire plant kingdom is as rich in silica as horsetail. It also rejuvenates the hair, adding sheen and strength to each strand. Horsetail also contains appreciable amounts of selenium and cysteine, important protein building blocks, which are known to prevent hair loss and promote hair regrowth. Both of these active agents also contribute to healthy hair follicle cells by preventing free radicals damage.