Flexi Says: Halogens are very reactive elements. This property makes them harmful to some microbes, thus chlorine, bromine, and iodine are often used for disinfecting solutions for industry, medicine, cleaning, and water treatment. These halogens are also used as oxidizers for rocket fuel. Bromine is commonly used as a fire retardant. Fluoride compounds are used in toothpastes and rinses to prevent dental cavities.