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 body, the Tenth Doctor was pleased to find he had longer hair than his previous incarnation, who wore his hair close-cropped, unlike his other incarnations who had had longer hair, exclaiming "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 found otherwise. As it was now long enough to pull in front of his eyes, he checked the colour and to dismay he was "still not ginger." (TV: The End of Time)

Some, such as several incarnations of the Master, chose to grow and style their facial hair.

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. (TV: The Name of the Doctor)