One thing that could cause spontaneous combustion is known as the “Wick Effect”. This is when body fat acts as a fuel source for the flames. The person would act as an “inside-out candle”, where the fat works as a fuel source and the clothing acts as a wick. The fat melts and seeps into the clothing, keeping a continuous source of fuel for the fire.
In 1998, a group of scientists decided to find an explanation for spontaneous combustion cases. So they took a dead pig and wrapped it in a blanket. They ignited it and it burned for five hours. When they looked at the remains, they found that it was very similar to the remains of those who died in spontaneous combustion cases. It confirmed the wick effect - showing how someone can catch on fire without the fire spreading or getting the attention from anyone who might be nearby.