When did they start spraying chemtrails?

The concept of chemtrails—allegedly harmful chemical substances sprayed from aircraft—gained popularity in the late 1990s and early 2000s, although the idea itself is based on conspiracy theories rather than scientific evidence. The trails observed behind planes are scientifically understood as contrails, formed from water vapor and exhaust. Various claims suggest government or military involvement in such spraying, but no credible evidence supports these theories. The spray patterns observed are typically the result of normal aviation activities and atmospheric conditions.