A man suffered "potentially life-changing injuries" and a woman also needed hospital treatment after the attack in Weymouth, Dorset.
The victim had liquid, believed to be acid, thrown in his face as he answered the door to two men in the Louviers Road area late on Sunday.
A 34-year-old man from Weymouth has been arrested.
Dorset Police said the people involved were believed to be known to each other.
One of the attackers was described as white, in his late 20s or early 30s, about 6ft-tall (1.83m) and of medium build. He had grade-one short hair and stubble on his face. He was wearing dark clothing.
The other was described as white, in his mid-20s to mid-30s and of large build. He had a moustache or goatee beard and what could be a London accent. He was also dressed in dark clothing.
Det Sgt Simon Austin, of Weymouth CID, said: "I am appealing to anyone who may have seen the two men, or has any information about the incident to contact police as soon as possible.
"Also, I would like to hear from anyone who may have witnessed any suspicious vehicles in the area at the time."
Police said the arrested man was being questioned on suspicion of conspiracy to commit grievous bodily harm with intent.
Two people have been injured in a suspected acid attack.