The fringe concept posits that airplane vapor trails, or contrails, are really “chemtrails” containing toxic substances that poison people and the terrain. Robert Michael/dpa/picture alliance/Getty Images

While plowing a wheat field in rural Washington state in the 1990s, William Wallace spotted a gray plane overhead that he believed was releasing chemicals to make him sick. The rancher began to suspect that all white vapor trails from aircraft might be dangerous.

He shared his concern with reporters, acknowledging it sounded a little like “The X Files,” a science fiction television show.

Academics cite Wallace’s story as one of the catalysts behind a fringe concept that has spread among adherents to the Make America Healthy Again, or MAHA, movement and is gaining traction at the

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