Chakwas mentions that she's discussed dermal regeneration with him, but he refused, as he seems to like his scars.
His Lair of the Shadow Broker dossier also reveals that he won't go on video chat with his sister since he was injured. When you're romancing him, when he tries to dissuade Shepard, he says: 'Look, Shepard, I'm not-' He stops there, but his hand is touching the scarred side of his face for a moment before he drops it. He appears to take his new scars well, but by speaking to Kelly or Garrus himself, you'll find out he's in serious pain (emotionally and physically) and just putting on a brave face for the sake of the mission.
