Sideburn

Sideburns were a variant of facial hair; they were thick patches of whiskers on the sides of one's head.

The Third and Fourth Doctor both wore sideburns (TV: Spearhead from Space, TV: Planet of the Spiders) - the Fourth's were red even though the hair on his head was dark brown. (PROSE: The Drosten's Curse) The Tenth Doctor was delighted to see he had grown sideburns after his regeneration. (TV: Born Again) He kept them to the end of his life, (TV: The End of Time) though he was once temporarily aged to a point he lost them, and later, all of his hair. (TV: The Sound of Drums, Last of the Time Lords)

The Tenth Doctor described the Fourth Doctor as being all "scarf and sideburns". (AUDIO: Out of Time)