A Halloween Riddle Poem by Patti Masterman

He's under my skin,
My well-hid friend,
An anorexic cast to him;
His bony pallor
Is ivory white-
He only looks
Well dressed at night.

He's always there,
Sealed off from air,
And he hasn't any hair;
He doesn't need
To groom at all,
But truth be told-
He casts a pall.

He doesn't mean
To make a scene,
Especially at Halloween;
Low-key is he,
He's in disguise:
You'll never see him-
Behind my eyes.

What is he?