There are no immediate symptoms related to Radon exposure. The only known health issue linked to Radon is lung cancer. Each year in the United States, it is estimated that more than 21,000 people die from lung cancer caused by exposure to Radon. Radon is the second leading cause of lung cancer in the United States behind smoking. There is no evidence suggesting that asthma, or any other respiratory disease, is linked to or caused by Radon.