Colloidal silver (a colloid consisting of silver particles suspended in liquid) and formulations containing silver salts were used by physicians in the early 20th century, but their use was largely discontinued in the 1940s following the development of safer and effective modern antibiotics.^[9][10] Since the 1990s, colloidal silver has again been marketed as an alternative medicine, often with extensive "cure-all" claims. Colloidal silver products remain available in many countries as dietary supplements and homeopathic remedies, although they have never been proven to be effective in treating any known condition. They also carry the risk of both permanent cosmetic side effects such as argyria and serious allergic reactions.^[11][12]