A woman was verbally abused before her attacker threw a substance at her which left her face and eyes "stinging and burning."
Police are appealing for information after the 35-year-old woman was targeted in Hartlepool.
The incident happened on Wednesday at 8.45pm when the victim was walking along Caledonian Road.
A Cleveland Police spokesman said: "A vehicle travelling from the direction of Oxford Road drove alongside her and an unknown person got out of the vehicle, verbally abused her and then threw a substance in her face.
"They then got back into the vehicle and drove off.
"Following the incident, the woman received medical treatment for stinging and burning to her face and eyes but there was no lasting damage.
"The substance was not acid."
Anyone who may have witnessed what happened or anyone with information regarding those responsible is asked to contact Detective Constable Phillip Lamb on the non-emergency number 101, Crimestoppers anonymously on 0800555111 or www.crimestoppers-uk.org.