Modern scientists are still investigating what might be behind reports of alleged spontaneous human combustion, but by the end of the 18th century, reports of humans suddenly going up in flames were pervasive enough that physicians compiled supposed risk factors for the phenomenon.

There have been many alleged cases of spontaneous human combustion in history — but such accounts tend to rouse suspicion even among the more open-minded of us. How is it possible, after all, for the human body to just simply explode into flame? Well, writing in New Scientist, biologist Brian J. Ford thinks he's found …

Some people say that spontaneous human combustion is just a regular fire that people can't be bothered to find the cause for, that could have been avoided through basic fire safety. Others say that it's just a peculiar shift of our internal chemistry, that can happen to anyone at any time.

This photograph from 1916 is of a fire at the Treasury Dept.'s "Bureau of Engraving and Printing," presumably in Washington, D.C. Mysteriously, however, whomever labeled it described the fire as "spontaneous combustion."