Don't know---but here is their "preferred formula": The Exclusive Formula Preferred use: Silver DiHydrogen Citrate formula for whole-space disinfection.* • Fully tested and approved by the US Environmental Protection Agency (EPA). • EPA rated Category IV for safety – does not require gloves, goggles or respirators. • EPA approved for Use on Children’s Toys and Food Handling Equipment – without wiping. * Steri-Phase technology can use other formulas. * Patent applied for special use. some background on SDC: http://www.virox.com/files_docs/content/pdf/en/download/Technical%20Bulletin%20on%20Silver-containing%20Germicides%20_2010_-%20New%20Format.pdf