Fog

The fog is a poisonous, corrosive vapour released by the Gamemakers in the 75th Hunger Games as one of hourly horrors. It is mentioned to look like an "after-rain fog" that then grows and becomes thick and acrid. It kills muscles and makes its victims twitch. The fog is made by the Gamemakers of the 75th Hunger Games.

Effects
The effects of the fog include itchy scabs, convulsions, and rapidly atrophying muscular tissue and sometimes death. Haymitch gives Katniss a thick, tar-like ointment to treat her scabs and she says that it feels very soothing, even though it turns her skin a sickly green color. Katniss accounts that when she was helping Peeta escape, the fog had reached one side of his face which caused the muscles on that side to collapse and die. Soaking in salt water relieves the effects of the fog.

Victims
Mags, the oldest tribute in the 75th Hunger Games, dies from the fog when Katniss's muscles start to convulse and can no longer carry her. Mags then willingly runs into the fog after giving Finnick Odair a quick kiss and immediately dies. Peeta, Finnick, and Katniss later suffer severe muscle damage by stray droplets of the fog.