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 silver proteins in purified water. Colloidal silver with concentrations of 30 parts per million (ppm) or less are typically manufactured using an electrolysis process, whereas colloidal silver with higher concentrations of 50 ppm or more are usually either silver compounds such as silver chloride and silver iodide or are solutions that have been bound with a protein to disperse the particles. Silver ions are reported to kill bacteria via the oligodynamic effect by inhibiting the expression of enzymes and other proteins essential to ATP production.
Prior to 1938, colloidal silver was widely promoted as a "cure-all", and silver products were prescribed by physicians as topical antibiotics. However, with the development more effective, less expensive antibiotics such as penicillin and sulfanilamide, medical use of colloidal silver ceased. From approximately 1990, 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.
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. Colloidal silver has been found to lack any antimicrobial effect, and 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 colloidal silver. There are no clinical studies in humans demonstrating effectivness, and several 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.
A number of case reports describe argyria after ingestion of colloidal silver marketed as an alternative-medicine treatment. Colloidal silver may theoretically interact with some medications, including tetracycline and quinolone antibiotics and penicillamine, reducing the effectiveness of those medications.
Following this ruling, the FDA has issued numerous warnings to Internet sites which have continued to promote colloidal silver as an antibiotic or for other medical purposes.
In 2002, the Australian Therapeutic Goods Administration (TGA) ruled that colloidal silver-containing products were no longer exempt from therapeutic goods legislation and had to meet the requirements of other products covered by this law. The TGA found that "there are no current legitimate uses of colloidal silver and that the Surveillance Section of the TGA be requested to investigate the illegal availability of colloidal silver products because of concerns about their significant toxicity. The reasons for the recommendation were that:
There is little evidence to support therapeutic claims made for colloidal silver products; the risk to consumers of silver toxicity outweighs the value of trying an unsubstantiated treatment, and bacterial resistance to silver can occur; and efforts should be made to curb the illegal availability of colloidal silver products, which is a significant public health issue.