Alopecia

Alopecia was the term given to hair loss. Hobo Kostinen had alopecia, (PROSE: Avatars of the Intelligence) which he had been bullied for. (PROSE: 8.46)

After the Time Lords resurrected him, the Master's new incarnation was totally bald. The Eighth Doctor ridiculed him because of it. (AUDIO: Eyes of the Master)

Behind the scenes
Matt Lucas, who played Nardole, has alopecia.