Your driveway could be making you sick. A new study by Oregon State University found products used to seal driveway surfaces could increase your risk of cancer. Instead of re-paving, parking lots and driveways are often repaired with a much less expensive sealant or sealcoat. The two most common kinds are a coal-tar-based sealant and one that's asphalt-based. Recent U.S. Geological Survey studies have shown that coal-tar-based sealants contain hazardous chemicals that have been linked to cancer.