A man sprayed bleach into the eyes of a Poundland worker when she asked him not to queue-jump, police have said.
Officers said the woman, 24, also had the liquid poured over her head in the attack at the shop in Wolverhampton.
She only escaped serious injury because quick-thinking colleagues helped remove clothing and rinse her skin, West Midlands Police said.
CCTV images have been issued of a man police want to speak to over the “serious assault”, on 5 January.
The customer of the store, in Wulfrun Square, sprayed bleach into the woman’s eyes and poured the remaining liquid over her head, causing burning and reddening to her eyes and body.
“Our investigations so far suggest that the incident occurred as the woman, who was working in the store at the time of the attack, requested that the man re-join his correct place in the queue after appearing to push to the front,” said Det Con David Firth.
“While her physical injuries will heal, we are certainly not underestimating the psychological impact this incident has had.”
Police say they are looking to speak to the man in the CCTV images, who is described as being white man, with short dark hair and stubble, about 5ft 6ins tall and slim.
Investigations are continuing and police have urged anyone with information, or who recognises the man, to come forward.