The Science of Spontaneous Human Combustion — The Wick Effect and Beyond

The most widely accepted scientific explanation for cases of apparent spontaneous human combustion is the 'wick effect' or 'human candle' theory. First proposed in the 19th century and experimentally validated in the 1960s, the theory posits that a fully clothed human body, once ignited by an external source (typically a cigarette, candle, or fireplace ember), can sustain prolonged combustion using its own subcutaneous fat as fuel and the clothing as a wick. The process is analogous to an inside-out candle: fat melts from the heat, is absorbed by the clothing, and burns slowly at a relatively low temperature (around 250°C) for many hours. This slow, sustained burn can destroy a body while leaving the surrounding room relatively undamaged, because the fire never reaches the open-flame stage that would ignite nearby objects. Experiments by Dr. John DeHaan of the California Criminalistics Institute using pig carcasses wrapped in cloth demonstrated that a body could burn for five to seven hours in this manner, reducing to ash and bone fragments in a pattern consistent with SHC cases. Critics acknowledge the wick effect but argue it requires an ignition source that is absent in some cases, and that the extremely high temperatures needed to shrink a human skull (as in the Mary Reeser case) exceed what the wick effect can produce.