90% of all lung cancer occurs in cigarette smokers, and an individual's risk of cancer increases in proportion with the number of cigarettes smoked. The risk of lung cancer decreases significantly some years after cessation of smoking. Other risk factors for lung cancer include inhalation of asbestos fibres, beryllium, nickel, chromium and excessive exposure to radiation. Other risks of smoking include accelerated atherosclerosis ("hardening of the arteries" possibly leading to heart attack, stroke or gangrene of the lower limbs), emphysema, chronic bronchitis, cancer of the larynx, oesophagus and bladder.