system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Spontaneous Combustion

How? Why do people spontaneously combustion?
gpt
Nobody really knows for sure, due to its weird nature. However, it is accepted that two things are needed: fuel and ignition.

Fuel is either methane produced from digested foods (farts) being excreted from the skin or oily body fat. An ignition is usually either static electricity or a cigarette.

Do not worry though, spontaneous human combustion is very rare and it usually occurs 'naturally' in humans that are obese or have severely imbalanced bodily fluids. It is also very unclear if it actually exists due to rarity.

EDIT: another theory for fuel is buildup of flammable substances (like alcohol) in the blood.