An 18-year-old man has been left with severe burns to his face, neck and shoulder which police said could be life-changing.
The man was talking to a 47-year-old woman at the time of the incident - she has been treated for minor burns on her shoulder and neck.
The attack occured at 1.10pm on Wednesday on Fulham Palace Road in west London when a man walked up to them and threw a corrosive liquid at the teenager, which splashed onto the woman.
It comes days after an acid attack at a Hackney nightclub left 20 people with chemical burns.
The suspect, who is described as a black male, then ran off down Crabtree Lane.
Police say he might have then fled the area on a moped that was parked of Bothwell Street.
Both victims were taken to a west London hospital to be treated.
They have both been discharged.
Police are appealing for anyone who witnessed the incident or has information related to it to come forward to call detectives on 020 8201 2889 or call Crimestoppers on 0800 555 111.