A second teenage boy is in custody after two males on a moped carried out five acid attacks across London in less than 90 minutes.
The teenagers - aged 15 and 16 - were arrested on suspicion of robbery and grievous bodily harm following the assaults in the north and east of the capital, which the Metropolitan Police said appeared to be linked.
Two involved victims having their mopeds stolen, while one victim has been left with "life-changing" injuries after being doused on Thursday night, the force added.
Chief Inspector Ben Clark, from Hackney Borough, said all of the victims were riding mopeds, adding that it is not the case that they were all food delivery riders.
Labour MP Stephen Timms, who will lead an adjournment debate on acid attacks in the Commons on Monday, has called for tougher sentences for those found guilty.
Acid attack survivor Katie Piper said victims face a "life sentence" as she also called on tougher sentencing to act as a deterrent.
The TV presenter, author and charity campaigner has undergone more than 250 operations after an ex-boyfriend arranged the assault nearly a decade ago.
In an open letter published in the Scars, Burns & Healing medical journal on Thursday, she revealed: "I couldn't recognise myself when I woke up from a coma and I wanted to commit suicide."
She added: "I will continue to need operations and therapy for life. For acid attack survivors, the aftermath is a life sentence."
Police said the 15-year-old was arrested at an address in Stoke Newington on Friday morning, while the 16-year-old was arrested in the early hours of Friday in Kingsbury Road after he was identified near the scene of the offences by local authority CCTV operators.
Both suspects are in custody at a north London police station.
Theresa May's spokeswoman said the Prime Minister viewed acid attacks as "horrific".
She told a Westminster briefing: "It is already an offence to carry acid or a corrosive substance with intent to cause harm. And anyone using it can be prosecuted for pretty serious offences including ABH and GBH.
"We are working with the police to see what more we could do.
"The Prime Minister's view is that the use of acid in this way is horrific."
Commissioner Cressida Dick revealed the Home Office is working with the Met to see if a change in the law is needed.
Chief Inspector Clark said: "This is a fast moving investigation and we have made two arrests today.
"However, I would like to ask the public for their help. Each of these offences took place in busy locations and we know there may be witnesses who have not yet contacted us. If you saw something or managed to film or photograph anything that might help us please get in touch.
"These are hideous offences and must have been very frightening for all of the victims.
"I'm aware of rumours circulating that the victims were all food delivery riders set up in advance of the attacks. This is not the case.
"All victims were riding mopeds at the time of the attacks, but were from a variety of backgrounds.
"Of late we have seen more attacks using corrosive substances in London. I would urge businesses and parents to challenge those who they think may be trying to obtain or carry these substances as this could help prevent serious offences and life-changing injuries being caused."
At 10.25pm on Thursday, police were called to Hackney Road junction with Queensbridge Road to reports of a robbery.
A 32-year-old man suffered injuries to his face after two male moped riders threw a corrosive substance in his face and stole the moped he was riding.
The two suspects then made off from the scene, with one on the stolen moped.
The man was taken to an east London hospital, and his injuries are not being treated as life-threatening or life-changing.
At 10.49pm police were called to St Paul's Road in Islington, near the border with Hackney, where a 44-year-old man riding a moped had a corrosive substance thrown in his face by two males, also on a moped.
The two suspects left the scene empty handed, and the victim was taken to hospital.
Police are awaiting an update on his condition.
At 11:05pm police were called to Shoreditch High Street where a 52-year-old man had a corrosive substance thrown in his face by two males on a moped.
The victim was also riding a moped but the suspects again got away empty handed.
The victim was taken to hospital and police are waiting for an update on his condition.
At 11:18pm police were called to Cazenove Road near the junction with Upper Clapton Road where a 24-year-old man was attacked in a similar way.
He was taken to an east London hospital where his injuries are described as "life-changing" .
At 11:37pm a 33-year-old man reported to police that he was on his moped in Chatsworth Road in traffic when two males on another moped pulled up alongside him and sprayed a liquid in his face before stealing his moped and making off.
The victim made his way home before contacting police.
He was taken to an east London hospital and police said they are waiting for an update on his condition.
One witness saw police pouring huge bottles of water over the first victim just outside her flat.
Sub-editor Sarah Cobbold, 29, told the Press Association: "I had thought someone must have chucked petrol or acid on him or something because they were covering him in water, but I have never seen that reaction to an attack, I thought maybe there had been an accident."
Asha Kaur, 26, said it was frightening to think that an attack happened so close to where she lives off the Upper Clapton Road.
The beauty therapist, who got home on Thursday night at 11pm - shortly before the attack - said: "It's just scary because I walk to work and it's just literally outside your doorstep."
A woman who lives in flats off Upper Clapton Road, who did not want to be named, said she heard shouting coming from outside, although she thought it was closer to 12.20am.
"I just saw blue flashing lights and heard a load of shouting," she said, adding that she heard someone shout "Oi, what do you think you're doing?"
She said: "I just thought it was a fight broke out because it was the time people would have been coming home from the pub."
Sandra Smith, 37, also lives in a flat off Upper Clapton Road and said: "It's a nice area. It's a multi-cultural area. Everyone gets on. We all mix.
"We've never faced anything like this. It's a quiet area. We never really get any problems, the odd petty crime.
"Everyone's quite shocked. An acid attack, you hear about it, but never close to home."
The attacks come just days after John Tomlin, 25, appeared in court accused of throwing acid at aspiring model Resham Khan, 21 and her cousin Jameel Muhktar, 37.
They were left with life-changing injuries after the attack on Ms Khan's 21st birthday in Beckton, east London.
One of the victims was a Deliveroo rider, a spokesman for the company said.
"These are truly shocking attacks and we are working with the authorities to help bring the perpetrators to justice," he added.
"We are in touch with the rider and will be providing him with support.
"We have been in touch with all riders who were working in these areas at the time of last night's attacks to check whether they were a victim of these horrific crimes and to gather further information that might help the police with their inquiries.
"We will be meeting with the police and other delivery companies to agree concrete action to keep our riders safe from this senseless violence."
Food delivery firm UberEATS also confirmed one of their drivers was a victim of Thursday night's attacks.
"All of us are shocked by this horrific and senseless attack," said Toussaint Wattinne, general manager of UberEATS in London.
"We have been in touch with the courier and offered to help him and his family in any way we can.
"We would like to thank all the couriers who rushed to help in the immediate aftermath of the attack.
"Our team has been contacting couriers in the area at the time, encouraging them to contact the police if they have any information which could assist them.
"We have spoken to the police and will do whatever we can to support their investigation."
Delivery driver Jabed Hussain told Sky News he was attacked at the traffic lights on Hackney Road on Thursday night.
He said: "I heard the sound of water, like a glass of water, come onto my face. I didn't realise it was a kind of acid or anything.
"I left my bike, I ran, I don't know how I managed to run. I was just begging for the water because at that time it was burning on my face.
"Then I started screaming. I felt like somebody put fire on my face, on the left-hand side."