A chemical that comes from certain substances when they are not burned completely. It is found in car exhaust, smoke from wood fires, tobacco, oil and gas products, charred or grilled foods, and other sources. It may also be found in water and soil. 3,4-Benzpyrene can cause a skin rash, a burning feeling, skin color changes, warts, and bronchitis. It may also cause cancer. It is a type of polycyclic aromatic hydrocarbon. Also called benzo(a)pyrene.