User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-6050823-20140101060000/@comment-5043481-20140101114056

If the old skin was powdery enough, then when the flapped thier wings it would float off in a cloud (like we see) and be easy to ignite. When on the dragon, this would presumably be compacted enough to not ignite easily at all. Like flour. try setting fire to a heap of flour and nothing will happen very much. But when suspended in air, it has massive surface area and so will burn easily and rapidly.

I guess this is why we don't see teos exploding all the time.