Health and Human Services Secretary Robert F. Kennedy Jr. faced widespread criticism after telling an anti-vaccine group that he is investigating "chemtrails," a widely discredited conspiracy theory. The statement was made during an event in Washington, D.C., where he addressed the anti-vaccine organization Children’s Health Defense, which he led from 2015 to 2023. Kennedy told the audience he is "looking at chemtrails and the impact of emissions from aircraft, and those potential impacts on health." He also mentioned his commitment to increasing "science transparency" around vaccine-related concerns. However, he did not provide any specific details about the scope or findings of the investigation. Chemtrails refer to the visible contrails—condensation trails—left by aircraft in the sky. These are formed when hot exhaust from jet engines mixes with cold, high-altitude air, creating ice crystals. These trails are harmless and typically evaporate quickly. Despite this, the term has been used in conspiracy theories suggesting that governments are deliberately spraying harmful chemicals from aircraft for secret purposes. These claims have been repeatedly debunked by scientific and governmental agencies. A 2016 study of 77 atmospheric scientists found that 76 of them had seen no evidence supporting the chemtrails theory. Kennedy's remarks drew sharp reactions on social media, particularly on X (formerly Twitter). Arizona Senator Mark Kelly, a former pilot and astronaut, responded by offering to send Kennedy an aircraft propulsion textbook, saying, "What you are suggesting is not real." Other critics quipped about the absurdity of the claim, comparing it to belief in mythical creatures like Bigfoot or the Loch Ness monster. Infectious diseases expert Dr. Neil Stone humorously suggested Kennedy might next investigate "leprechauns and unicorns" and called him "a fool." Even some conservative commentators expressed disbelief at the comments, with one noting that even right-wing individuals were likely rolling their eyes at the remark. RFK Jr., a former environmental lawyer and member of the prominent Kennedy family, rose to public prominence during the Covid-19 pandemic by promoting anti-vaccine sentiment and spreading conspiracy theories about public health institutions. Despite lacking a background in medical science, he has made a range of controversial claims, including that a parasitic worm once devoured part of his brain and that he once beheaded a beached whale with a chainsaw. Under his leadership, the Department of Health and Human Services has been accused of alienating top scientists and endangering children by altering vaccine administration protocols, such as splitting the MMR vaccine into three separate shots.