Contrary to what you might think, horsetail does not, in fact, come from a horse's ass. Horsetail, a plant that is fernlike in quality, has been used since ancient Greek and Roman times for medicinal purposes, such as healing cuts and treating tuberculosis.
As far as beauty is concerned, the extracts from the horsetail plant help stimulate the skin and the production of elastin and collagen and protect the skin from oxidation. Hence, you'll often find this ingredient in antiaging products. This restorative ingredient not only helps to tone the skin but is also used to help repair brittle fingernails. Try Honeybee Gardens Odorless Nail Polish Remover ($7) or The Glacial Facial Masque ($34) by Alaska Glacial Mud Company.
Source: Flickr User Richardmasoner