Cigarettes are often seen as the source of fire in alleged cases of Spontaneous Human Combustion. Improper disposal of smoking materials causes one in every four fire deaths in the United States. Natural causes such as heart attacks may lead to the victim dying, subsequently dropping the cigarette, which after a period of smoldering can ignite the victim's clothes.
One suggested phenomenon that could account for spontaneous human combustion is ball lightning. According to one scientist, the charring of human limbs seen in a number of ball lightning cases is very suggestive that this mechanism may also have occurred where people have had limbs combusted.
Ketosis can explain alleged mysterious cases of Spontaneous Human Combustion. Ketosis, possibly caused by alcoholism or low-carb dieting, produces acetone, which is highly flammable and could, therefore lead to spontaneous combustion.
Sometimes there are reasonable explanations for the deaths alleged to Spontaneous Human Combustion, but most of the times it has been found that proponents ignore official autopsies and contradictory evidence, in favor of anecdotal accounts and personal testimonies.
Two-year forensic investigation conducted in 1984 looked into the alleged Spontaneous Human Combustion cases of 18th to 20th centuries. Investigators found that the burned bodies were in close proximity to plausible sources for the ignition: candles, lamps, fireplaces, etc. Such sources were often omitted from published accounts of these incidents, presumably to deepen the aura of mystery surrounding an apparently "spontaneous" death. A correlation was found between alleged SHC deaths and the victim's intoxication.