Bleach was thrown at a woman in her 20s from a moving vehicle in King’s Lynn.
The female driver was travelling on the A149, between Hardwick and the Queen Elizabeth Hospital, in a silver Toyota when the attack happened at around 1.15pm yesterday (Thursday).
In an appeal for witnesses, police said the woman had the window open when she was hit by liquid, later found to be bleach, thrown by the occupants of a passing car.
The other vehicle is believed to have been burgundy in colour.
A police spokesman said the victim was treated at the QEH, but her injuries were not serious.
Anyone with information is asked to contact PC Kirsty Maynard at Lynn Police Station on 101, quoting crime reference 36/40335/21.
Alternatively contact Crimestoppers anonymously on 0800 555 111.