The 37-year-old victim was believed to have been deliberately targeted, reportedly with acid, in the attack in Edinburgh.
She suffered serious burns to her face and neck and was taken to hospital where she continues to be treated.
Police are hunting for a man who carried out the assault on Captain's Road in the southeast of the city around 8.40pm on Friday evening.
The suspect is described as being aged in his early 20s, 5ft 11in tall, and of slim build.
His face was covered and he wore a grey hooded top, a dark tracksuit, dark gloves and dark trainers with reflective panels.
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Detective Inspector Stevie Rosie from Police Scotland said: "We are still working to establish the motive surrounding this attack.
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"However, we believe this to be a targeted attack. Police are supporting the victim, who has sustained some very serious injuries to her face and neck.
"Anyone who recognises him, or who has any other information relevant to this investigation should contact police immediately."