Plant extract that has a high tannin, alkaloid, and nicotine content, which can have skin-constricting properties and be irritating to skin. Horse tail extract also has antioxidant and anti-inflammatory properties. Unfortunately, there’s no real research proving these effects when applied to skin.
Gründemann C, Lengen K, Sauer B, Garcia-Käufer M, Zehl M, Huber R. Equisetum arvense (common horsetail) modulates the function of inflammatory immunocompetent cells. BMC Complement Altern Med. 2014;14:283.