Radon is a colorless, odorless radioactive gas that seeps up from the earth. When inhaled, it gives off radioactive particles that can damage the cells that line the lung. While radon is present everywhere, and there is no known, safe level, your greatest exposure is where it can concentrate-indoors. And where you spend most time-at home. Your home can have radon whether it be old or new, well-sealed or drafty, and with or without a basement.