Toronto police are looking for a woman who allegedly sprayed an unknown substance on a passenger while riding a TTC bus on Thursday.

At approximately 6:10 p.m., police said, officers responded to an assault onboard a bus which was located at Sheppard Avenue East and Markham Road at the time.

Police said the suspect and victim were travelling eastbound before the suspect exited the bus via the rear doors and sprayed the victim with an “unknown irritant.”

The substance caused a burning sensation, similar to pepper spray, police said.

The suspect fled the area on foot and the victim was treated by medics at the scene.

The suspect is described by police as a woman between 20 and 30 years old, with shoulder length brown curly hair.

Anyone with information related to the investigation is asked to contact police at 416-808-4200 or Crime Stoppers.