Colloidal silver is a colloid of silver particles in water. It has some antimicrobial properties, and is claimed by some to be a beneficial nutritional supplement. The ingestion of colloidal silver in large quantities or over a long period of time may cause the discoloring condition argyria, in which the skin turns blue-gray.
Properties
Colloidal silver can be used to keep drinkable water potable over a long period; however, it is not suited for disinfection. It is also used internally and externally for alleged health benefits. Colloidal silver has been claimed to kill various microorganisms. Continued ingestion of silver may result in argyria, a permanent discoloration of the skin.
While high concentrations of colloidal silver will certainly kill many bacteria in vitro, the use of colloidal silver as an internal (in vivo) medicine is controversial.
Due to unsubstantiated health claims (not having gone through the FDA's drug trial and testing regimen) and the poor quality of samples gathered in health food stores, in 1999 the US FDA banned over-the-counter sales of such products, or their advertisement as providing health benefits. If no health benefits are claimed, and colloidal silver is sold as a supplement, its sale is legal. In 2002, the Australian Therapeutic Goods Administration made a similar ruling [1].
Controversy
Avid users of colloidal silver claim it to be a very useful supplement to their diet, providing them with improved health and wellbeing and (among other things) a very low incidence of colds and flu. They also assert that, under careful use of properly produced colloidal silver, argyria is virtually impossible. These claims are testimonial, and have not yet been confirmed or refuted by scientific study.