The study by the National Academies of Sciences comes after dozens of U.S. diplomats in Cuba and China complained of migraines, dizziness and memory loss.
Nearly two years after the U.S. said diplomats in Cuba had been injured in a series of "health attacks," many scientists say there's still no proof anyone was injured.
Unexplained illnesses afflicting employees of the U.S. embassy in Havana led to the State Department decision to scale back staff and ban personnel's family members.