Alopecia

Alopecia was the term given to hair loss. (PROSE: Avatars of the Intelligence)

When he had grown quite older, the First Doctor appeared to have some degree of baldness, with most of his hair growing around the back of his head. (TV: An Unearthly Child)

The Fifth Doctor gained a temporary bald spot when the time differential in a future version of his TARDIS caused him to age very quickly. (TV: Time Crash)

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)

When the Tenth Doctor was forced to age by the Master, he went partially bald. The second time he was aged, he went completely bald. (TV: The Sound of Drums, Last of the Time Lords)

Hobo Kostinen had alopecia. (PROSE: Avatars of the Intelligence)

Though Nardole appeared to be bald, (TV: The Husbands of River Song et al.) his glass avatar would claim that he actually had invisible hair. (TV: Twice Upon a Time)