The chemtrail conspiracy theory is based on the erroneous belief that long-lasting condensation trails, called "chemtrails" by proponents, consist of chemical or biological agents left in the sky by high-flying aircraft and deliberately sprayed for purposes undisclosed to the general public.

Believers in the conspiracy theory argue that normal contrails dissipate relatively quickly and contrails that do not dissipate must contain additional substances. Those who subscribe to the theory speculate that the purpose of the chemical release may be solar radiation management, weather modification, psychological manipulation, human population control, or biological or chemical warfare and that the trails are causing respiratory illnesses and other health problems.

I must state that I don't believe in the chem-trail conspiracy theory because I feel it's very childish and immature.

There is no evidence that purported chemtrails differ from normal water-based contrails routinely left by high-flying aircraft under certain atmospheric conditions. Although proponents have tried to prove that chemical spraying occurs, their analyses have been flawed or based on misconceptions. Because of the persistence of the conspiracy theory and questions about government involvement, scientists and government agencies around the world have repeatedly explained that the supposed chemtrails are in fact normal contrails

*Pls note that the word chem-trail is a combination of two words : chemical and trail while contrail is also a combination of condensation and trail.