Two members of the staff and one customer were taken to hospital following the mid-air incident today.
Flight AA729 took off just after 11am for Philadelphia, Pensylvannia.
But the flight only just made past the island of Ireland when the pilots had to turn around and make an unscheduled landing in Dublin.
A spokesman for American Airlines said: “American Airlines flight 729 from London Heathrow to Philadelphia diverted to Dublin due to an odor caused by a spilled cleaning solution in the galley.
“The flight landed safely in Dublin at 1.15pm local time, and taxied to the gate.
“Medical personnel have met the aircraft to evaluate any crew members or passengers who may need additional assistance."
“Two crew members and one customer were taken to the hospital for evaluation,” the spokesman added.