There are a couple things we know about what Master Chief keeps under his helmet, he's a caucasian male with reddish-brown hair. Now, have we ever really seen his face? Not really. If you completed Halo 4 on Legendary then you got a glimpse of his eyes, but that is it.
Things won't be changing in Halo 5: Guardians in that respect. We still won't be seeing Master Chief's face, but we really don't need to — he's the Chief, no matter what.
According to Halo 5's creative directive Tim Longo, Master Chief will leave his helmet on for the entire campaign. You've got to imagine how sweaty and smelly the inside of his helmet is by now. “I actually don’t even know if I can talk about that… He doesn’t take his helmet off,” said Longo to Gamerant.
This only leads me to believe that when Chief takes off his helmet there will be another helmet underneath.
Halo 5: Guardians is set to arrive exclusively for Xbox One on October 27, 2015.
