The guy felt some liquid burning through his trousers as he travelled during the rush hour and told the staff at Holland Park Tube station. He was taken to hospital and treated for minor skin irritation.
The Press Association report "Two trains were immediately taken out of service and underwent thorough searches, Transport For London said.
A spokeswoman for British Transport Police said: "We are not treating this as being malicious at this point.
"From our inquiries it seems that some sort of cleaning fluid has been spilled accidentally.
"The man was taken to Chelsea and Westminster Hospital suffering from skin irritation. There was some damage to his trousers."
Just as well it didn't happen in the summer time when people may have been wearing far fewer clothes.