Which two chemical elements are most commonly used as disinfectant or antiseptic?

These two powerful germ-killers both belong to the halogen group on the periodic table, a family of elements known for their high reactivity. Chlorine is perhaps the most widespread disinfectant, famously used to purify swimming pools and public drinking water supplies. It works by acting as a powerful oxidizing agent, effectively breaking down the cell walls and essential proteins of bacteria and viruses, rendering them harmless. Its life-saving properties were dramatically demonstrated in the 19th century when it was used to decontaminate the water source responsible for a deadly cholera outbreak in London.

Its fellow halogen, iodine, is typically used as an antiseptic, meaning it is applied to living tissue to prevent infection. You might recognize it as the brownish solution, often in the form of povidone-iodine, used to sterilize skin before surgery or to clean minor wounds (Review). Like chlorine, iodine penetrates microorganisms and fatally disrupts their cellular structures and functions. While highly effective at killing pathogens on the outside of the body, iodine is also an essential nutrient required by the thyroid gland on the inside.