Silver is a natural antibiotic. It is active against bacterias, viruses, fungis or parasites. Silver inhibits the growth and reproduction of bacterias. Silver's antibacterial activity is so outstanding that it has been selected among twenty products to treat and purify U.S. space program's water. The properties of this noble metal have never been so sought after: in the 2000s more than 500 tons of nano-silver were produced every year in the world in the form of silver ions, silver proteins or colloids so to be used in the cosmetic, medical or industrial fields.