A woman suffered chemical burns in a “terrifying attack” in which a gang of youths threw a corrosive liquid in her face.
The 21-year-old was confronted by eight people at 6.20pm on Monday in Wright Close, Newton Aycliffe.
It is believed they ran towards the town centre after throwing the liquid at their victim.
Durham Police said the white foam-like substance smelled like bleach and caused the woman’s skin to peel off.
Insp Sarah Honeyman said the substance had burned the victim but officers did not yet know exactly what it was.
She added: “From the victim’s point of view it was a terrifying incident, particularly in view of acid attacks in London and the devastating consequences of those attacks.”
The force is appealing for anyone with information to come forward by calling 101.