Smoking causes many serious and fatal diseases and conditions including lung cancer, chronic obstructive pulmonary disease (COPD), heart disease, bronchitis and emphysema. It also causes many other cancers, respiratory diseases and strokes, and can affect fertility. Cigarettes contain over 4,000 toxic chemicals and around 50 of these cause cancer. Carbon monoxide is a poisonous gas in cigarette smoke. It is also found in car exhaust fumes and produced by faulty gas appliances. It takes the place of oxygen in the blood, causing your lungs to work less efficiently. This stops cells all around your body from getting the oxygen they need. Tar is the sticky brown substance that stains your fingers and teeth. Tar causes cancer and damages your lungs. It stays inside your lungs, making tubes narrower and reducing your protection against infection.