Shawkat Hussain, 24, and his friend (unidentified) ran screaming in agony into an off-licence in Bethnal Green and begged for help after being sprayed with corrosive liquid.
Dramatic footage shows the pair in their underwear being washed down by firefighters and paramedics in front of shocked passers-by.
Hussain’s sister Zakia, 22, shared pictures of her brother’s life-changing facial injuries, and told journalists: “I just don’t understand what these people are thinking, what are they getting from it? How can they just go around throwing acid at people?
“It’s going to be so hard for my brother from now on. You can see already that it has completely changed his appearance. He is devastated.”
The attack – the latest in a series of similar incidents this summer – took place at around 7pm on Roman Road in Tower Hamlets, east London on Tuesday.
According to witnesses, the victims were running with the burning liquid on their clothes and faces. A shopkeeper poured water over the pair while they waited for an ambulance to arrive.
They were treated at the scene before being taken to hospital.
Witness reports stated the pair were shouting: “We have got acid on us, we have got acid on us.”
The shopkeeper added: “They were pouring water over themselves and it had got into their clothes. They were crying, ‘put water on me’. Their faces and their legs were all burnt.”
Another witness, who did not want to be named, said the pair had stripped down to their waists on the street and were helped by passersby as they waited for the emergency services.
Pictures on social media show the men being helped by firefighters.
The number of reported attacks using acid has leapt in recent months, with a reported 65% rise in 2016, when there were 450.
Speaking about the incident on Wednesday evening, a Metropolitan police spokesman said: “Police in Tower Hamlets are dealing with a suspected noxious substance attack on two males in Roman Road, E2.
“Officers were flagged down in the area at 7pm on Tuesday, 25 July by the two males who are believed to be aged in their late teens.
“London Ambulance Service attended the scene.
“Both have been taken to an east London hospital for treatment after an unknown liquid was thrown at them.
“No arrests have been made. Enquiries are ongoing.”