More than a million Americans have Parkinson's disease, which is more than the number of people diagnosed with multiple sclerosis, muscular dystrophy, and Lou Gehrig's disease combined. Parkinson's kills brain cells that produce dopamine, a nerve-signaling chemical that helps control muscle movement, resulting in tremors and impaired movement and balance. But the triggers for this neurodegenerative condition aren't well understood. A growing amount of research suggests that exposure to pesticides may increase the risk for Parkinson's. Now an analysis of more than 100 studies from around the world offers more evidence. The findings, published May 28, 2013, in Neurology, suggest that exposure to bug and weed killers is associated with a 33% to 80% increase in risk of developing Parkinson's disease. "This is important; if we know more about what may be contributing to Parkinson's, we can create better treatments and develop better ways to prevent it," says Dr. Suzanne Salamon, a geriatrician and instructor at Harvard Medical School. "If you use pesticides, you should actually read and carefully follow the safety instructions on the label when handling and applying them," says neurologist Dr. Michael Schwarzschild, an associate professor at Harvard Medical School. These instructions usually call for wearing protective clothing, including rubber gloves, and washing well afterward to minimize exposure, especially ingestion.