PERC (Perchloroethylene) has been in use since the 1940's. Perc is the most common solvent and most aggressive cleaner. It can cause color bleeding/loss, especially at higher temperatures, and may destroy special trims, buttons, and beads on some garments. Better for oil-based stains (which account for about 10% of stains) than more common water-soluble stains (coffee, wine, blood, etc.). Perc is known for leaving a characteristic chemical smell on garments. A recent study conducted at Georgetown University shows perc, classified as carcinogenic to humans by the EPA, is retained in dry-cleaned clothes and that levels increase with repeat cleanings.