A forehead was a body part.
After Davros lost his vision, he used a blue lens on his forehead to see, similar to a Dalek eyestalk. (TV: Genesis of the Daleks, The Witch's Familiar, et al.) He was also capable of opening his true eyes, at least later in life, though he seldom made use of this ability. (TV: The Witch's Familiar)
Human skin suits used by the Slitheen were fitted with zips on their foreheads. (TV: Aliens of London/World War Three et al.) In reference to this, the Tenth Doctor asked Donna Noble if her fiance was "a bit overweight with a zip around his forehead." (TV: The Runaway Bride)