Colloidal silver is a liquid suspension of microscopic particles of silver. A colloid is technically defined as particles which remain suspended without forming an ionic, or dissolved solution. The broader commercial definition of "colloidal silver" includes products that contain various concentrations of ionic silver, silver colloids, ionic silver compounds or bound proteins in purified water. Colloidal silver with concentrations of 30 parts per million (ppm) or less are typically manufactured using anelectrolysis process, whereas colloidal silver with higher concentrations of 50 ppm or more are usually silver compounds that have been bound with a protein.

Colloidal silver is currently marketed for internal and external use as an alternative medical remedy though there is no scientific evidence to support its effectiveness in vivo. Most in vitro studies demonstrate an anti-bacterial effect of electrically generated silver ions, although a study of a colloidal silver solution marketed on the Internet showed no such antimicrobial activity. Excessive ingestion of colloidal silver can result in argyria, a condition in which the skin irreversibly turns blue or grey.

Historical applications

Silver has had some medicinal uses going back for centuries. In the early 1900s, silver gained regulatory approval as an antimicrobial agent. However, the use of silver diminished with the introduction of antibiotics in the early 1940s. A few prescription drugs containing silver are still available. Prior to 1938, colloidal silver was used as a germicide and disinfectant. Physicians used it as an eyedrop for ophthalmic problems, for various infections, and sometimes internally for diseases such as tropical sprue, epilepsy, gonorrhea, and the common cold.

Current applications

From approximately 1990, especially with the emerging problem of antibiotic resistance, there has been a resurgence of the promotion of colloidal silver as an alternative medicine treatment, marketed with claims that it can prevent or treat numerous diseases. In vitro evidence of an antimicrobial effect of colloidal silver is mixed; one study has found it to lack any antibacterial effect, while others have reported colloidal solutions of 5-30ppm as being effective against staphylococci and E.coli There have been no clinical trials showing that any preparation of colloidal silver is effective in vivo.

In research with E.coli using an aqueous solution with a silver ion concentration of 900 ppb (.9 ppm) electrolytically prepared by applying a current of 12.5 mA for 28 s between two silver plate electrodes in water, it was shown that one of the major bactericidal actions of the silver ion is caused by its interaction with the ribosome and subsequent suppression in the expression of enzymes and proteins essential to ATP production.

Colloidal silver products are legally available at health food stores in the United States and Australia and are marketed over the Internet as a dietary supplement. It is illegal in the U.S. and Australia for marketers to make claims of medical effectiveness for colloidal silver, but some websites still list its use for the prevention of colds and flu, and the treatment of more serious conditions such as diabetes, cancer, chronic fatigue syndrome, HIV/AIDS, and tuberculosis, among other diseases. There is no medical evidence that colloidal silver is effective for any of these claimed indications. Silver is not an essential mineral in humans; there is no dietary requirement for silver, and no such thing as a silver "deficiency".

Currently, there are no evidence-based medical uses for ingested colloidal silver. There are no clinical studies in humans demonstrating effectiveness, and a few reports of toxicity. The U.S. National Center for Complementary and Alternative Medicine has issued an advisory indicating that the marketing claims made about colloidal silver are scientifically unsupported, and that the silver content of marketed supplements varies widely and can pose risks to the consumer.