Wear it in Smoke Dungeon or you will receive damage. Also required to be worn while fighting Dust Devils regardless of location.
Level 10 Slayer is required to wear it. Can be combined with earmuffs to make masked earmuffs after starting Smoking Kills quest. Can be combined with spiny helmet, earmuffs, black mask and nosepeg to make slayer helmet after Smoking Kills quest and purchasing the ability from a Slayer Master.