Feline hyperthyroidism is the most common endocrine-related disease of older cats, and its prevalence has skyrocketed since the first case was diagnosed in 1979. At the same time, new household flame retardants were introduced, and recently, scientists have suspected a link. Now, researchers have associated hyperthyroidism with another class of flame retardants, using silicone pet tags similar to the popular wristbands that many people wear for charitable causes.