Colloidal Silver is a suspension of silver in water, typically 30ppm, which is either ingested or applied topically. The antibacterial properties of silver are well known – solutions as low as 5 ppm can kill many types of bacteria and fungus, and colloidal silver is approved by the EPA as a disinfectant for use in hospitals. You might be more familiar with silver-impregnanted hiking socks, which allegedly prevent foot odor by killing bacteria.
Prior to 1938 colloidal silver was a widely used antibiotic prescribed by physicians, but the discovery of fast-acting penicillin rendered it obsolete. Colloidal silver is still used in alternative medicine, and the FDA allows it to be sold as a supplement, but sellers are not allowed to make any medical claims about the benefits of colloidal silver. It is often marketed as a panacea-type supplement, and will supposedly cure anything from allergies to skin problems to arthritis.
One of the more startling possible side effects from the ingestion of silver is a marked skin discoloration called argyria, characterized by permanent blue discoloration of the skin. Extra silver is deposited in body tissue, and when exposed to sunlight the skin turns a dark blue or gray color ( the skin reacts much like the silver on a black and white photographic print does).
you can see a video of a man with argyria being interviewed by Matt Lauer on the Today Show: