Perfluorobutanesulfonic acid (PFBS) is a chemical compound with a four carbon fluorocarbon chain and a sulfonic acid functional group. As an anion it functions as a stable fluorosurfactant because of the strength of carbon–fluorine bonds. PFBS has served as a replacement for the persistent, toxic, and bioaccumulative perfluorooctanesulfonic acid (PFOS) in 3M's Scotchgard stain repellents since June 2003. PFBS has a much shorter half-life in people than PFOS (a little over one month vs. 5.4 years). PFBS is persistent in the environment. Studies have not yet been specifically conducted to determine safety in humans. 3M markets surfactant with PFBS in two fluorosurfactants.