Hair

Hair was a part of the anatomy that grew all over the body on many creatures and beings, mostly mammals. Humans and other similar species grew hair in all manner of places except for the soles of their feet and the palms of their hands. Mr Grange had hair growing out of his ears. (PROSE: Time and Relative)

After regenerating from his ninth incarnation, the Tenth Doctor was pleased to find that he had longer hair than his previous incarnation. The Ninth Doctor had worn his hair close-cropped, unlike his other incarnations who had had longer hair. The Tenth Doctor happily exclaimed, "I'm not bald!" (TV: Children in Need Special) Later on, however, he would be disappointed to be told that his hair wasn't ginger. (TV: The Christmas Invasion) After his next regeneration, the Eleventh Doctor, whose hair was even longer, initially believed that he was "a girl" due to its length; he quickly determined otherwise. As it was now long enough to pull in front of his eyes, he checked the colour and to his dismay found he was "still not ginger." (TV: The End of Time)

Some, such as at least two incarnations of the Master, grew and styled their facial hair. (TV: Terror of the Autons, The Mind of Evil, The Keeper of Traken, Logopolis) This beard became a trademark factor associated with the Master, such that the Fifth Doctor asked his future self if the Master still exhibited this trait. (TV: Time Crash)

Strax, a Sontaran without any hair on his own head, didn't understand the growth of hair on humans and other species; he once mistakenly thought River Song's curly hair meant she had a big head. Clara Oswald subsequently referred to River as "the lady with the funny name and the space hair". (TV: The Name of the Doctor)