Caused by breathing carbon monoxide (CO), which is formed during the incomplete combustion of many fuels. CO combines (in preference to oxygen) with haemoglobin in the red blood cells, making the transport of oxygen impossible. The symptoms of sudden poisoning are headache, dizziness, nausea, vomiting and lowered consciousness. The skin turns red. Severe cases can lead to heart damage, unconsciousness (coma), and cessation of respiration, often leading to death. Gradual poisoning is associated with headaches and other symptoms include sweating and constriction of the chest. Treatment is by administration of oxygen, possibly with artifical respiration in a high-pressure chamber, thus driving out CO from the haemoglobin. The patient gradually brightens up with treatment; there may be residual symptoms such as muscular quivering (tremor), and symptoms similar to paralysis or Parkinson’s disease; serious cases may lead to permanent dementia. Diagnosis is by the symptoms and the presence of excess CO-haemoglobin in the blood.