Gas stoves and ovens emit harmful chemicals, even when not in use, say scientists in California. Researchers found at least 12 dangerous air pollutants, including benzene, which is known to cause cancer in people with long-term exposure. The study's authors took air and gas samples from 159 California residences. Ninety-nine percent of the samples showed benzene. The scientists also calculated the exposure to benzene per household based on the size of the kitchen, the level of ventilation in the room, the amount of the substance and whether the stoves gave off gas leaks when they were turned off. The results showed that the most "leaky" stoves exposed people to benzene indoors at 7 times the California limit of safe levels. Over time, such exposure can increase the risk of blood diseases or respiratory problems, although scientists are still investigating exactly how benzene affects our health.