The Toxic Jungle was formed during an apocalyptic war known as the Seven Days of Fire. And it is hinted by Nausicaä, to be the cause of it's extremely polluted soil, as she claims it to be the result of man's destructive ways. Despite this, the only things that can grow there are fungi which produce spores that are poisonous to humans, as a result anyone who enters it must wear a gas mask. In many ways it acts like a desert, as the spores produced in the Jungle have spread across the world destroying the surrounding environments as they transform them into a part of it. Surprisingly, underneath it is an area with non-toxic air and pure, drinkable water, which is the result of the fact, that the Toxic Jungles plants actually purify the polluted topsoil.