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)

Historians who had been allowed access to the "Monster Vaults" of the databanks in the Doctor's TARDIS observed that Abzorbaloffs sported a Mohican-style tuft of hair. (PROSE: The Monster Vault, TV: Love & Monsters)

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: Born Again) Later on, however, he was disappointed to be told that his hair wasn't ginger. (TV: The Christmas Invasion) He decided to try back-combing it for a while, (TV: Fear Her) but later switched to spiking it up. Wilfred Mott used it as an identifying feature of the Doctor while the Silver Cloak was searching for him. He referred to it as "modern sort of hair, all sticky-uppy." (TV: The End of Time)

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)

The Eighth Doctor had long locks of hair after regenerating, but cut it down later in his life. (TV: Doctor Who, AUDIO: Tangled Web) It had grown back close to its original length when he regenerated. (TV: The Night of the Doctor)

Melody Pond was excited after regenerating into her third and would-be final incarnation when it came with a very large amount of hair. (TV: Let's Kill Hitler)

Mutation into a Primord from exposure to Stahlman's ooze caused humans to begin growing large amounts of hair on their bodies. A sign that the transformation was beginning was excessive hair growth on the hands, and later, the face. (TV: Inferno)

Curly hair was considered by Putta Pattershaun 5 to be attractive to women, and straight ginger hair unattractive to them. (PROSE: The Drosten's Curse)

Nardole had invisible hair, which his glass avatar claimed the Testimony Foundation had gotten "a bit wrong". (TV: Twice Upon a Time)

Facial hair
Facial hair was the presence of hair on one's chin, upper lip, or temples.

Some, such as SIX incarnations of the Master, grew and styled their facial hair. (TV: Terror of the Autons, The Mind of Evil, The Keeper of Traken, Logopolis, The King's Demons, The Five Doctors, Survival, Only the Good, The Master of Callous, Day of the Master, World Enough and Time, The Doctor Falls, Spyfall, Ascension of the Cybermen, The Timeless Children, etc.) 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)

Some incarnations of the Doctor also ended up with facial hair, but not always out of preference. Sometimes they were aged to the point it caused the unnatural growth of a beard, or they grew one from being kept in captivity with no way of shaving their hair. (TV: The Leisure Hive, Day of the Moon, The Wedding of River Song, The Day of the Doctor)

The Fifth Doctor grew a beard while he was stranded in London from 1866 to 1867 to make himself appear older and fit in with the scientific community. (AUDIO: The Haunting of Thomas Brewster)

The Eighth Doctor had facial hair during multiple periods of his life. He grew a beard shortly before his wedding to Scarlette (PROSE: The Adventuress of Henrietta Street) until later shaving it. (PROSE: Hope) He had a consistent state of facial hair while he was stranded on Orbis for six hundred years. (AUDIO: Orbis) In the later years of his life, he started to grow stubble on his face. (TV: The Night of the Doctor)

Both the Ninth and Tenth Doctors often had five-o-clock shadows and were said to shave. (TV: The Doctor Dances, Time Crash)

The Tenth Doctor was able to stop a beard growing through sheer concentration when he was incarcerated on Hurala for five days, but at the consequence that his chin would itch severely later on. (PROSE: Prisoner of the Daleks)

The Eleventh Doctor grew a beard during the three months he was acting as a prisoner in Area 51. He later shaved it. (TV: Day of the Moon)

When he became elderly, the War Doctor grew out a full beard. He maintained this beard up to his regeneration. He was chided with the nickname "Granddad" by the Eleventh Doctor because of his resemblance to a curmudgeonly old man. (TV: The Day of the Doctor)

Ian Chesterton shaved his face and had his hair cut from a special static electricity-powered shaver owned by the First Doctor - he considered its performance to be as good as a top-class professional barber. (PROSE: Doctor Who in an Exciting Adventure with the Daleks)

Moustache
A moustache was a variant of facial hair that grew on the upper lip.

Brigadier Lethbridge-Stewart sported his trademark moustache for most of his life. (TV: The Web of Fear, The Invasion, Spearhead from Space, The Silurians, Day of the Daleks, Battlefield, etc) However, his Inferno counterpart, the Alastair Lethbridge-Stewart, lacked a moustache and a left eye. (TV: Inferno)

Sideburns
Sideburns were another 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: Children in Need Special) 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)

Greying hair
For some species, such as humans, hair would turn grey, or sometimes entirely white with old age. Various incarnations of the Doctor experienced grey hair. Some, such as the Third Doctor (TV: Spearhead from Space) and Twelfth Doctor, (TV: The Time of the Doctor) had it immediately upon regeneration. Each case involved a regeneration where the face the Doctor took was not brand new, but deliberately modelled to look like an aged individual, the former being the Time Lords' doing as part of an imposed exile sentence, (TV: The War Games) the latter apparently being the Doctor's own doing. (TV: Deep Breath) Others lived to the point their hair went grey, or in the case of the First Doctor, white. (TV: An Unearthly Child, The Day of the Doctor, The Time of the Doctor, PROSE: Not in My Back Yard) Some were forced to age to the point of grey hair. (TV: The Leisure Hive, The Sound of Drums, Last of the Time Lords)

In rare cases, traumatic events could result in hair turning grey. The Second Doctor's encounter with the Players caused his hair to do such. (PROSE: World Game)

Stuart Hyde's hair went grey when the Master's use of TOMTIT caused a side effect that accelerated his natural ageing. Likewise, TOMTIT's continued use reverted him back to his normal age. (TV: The Time Monster)

The Fourth Doctor once referred to the Third Doctor's head as an 'old grey model' because of his hair colour. (TV: The Brain of Morbius)

Jack Harkness, after becoming immortal, still exhibited grey hair as he grew older. (TV: Last of the Time Lords) In the far future, at a time where the Vampires thought the Time Lords to be myths, Jack's hair had turned completely grey. (AUDIO: Mighty and Despair)

Other references
Vivien Rook met Lucy Saxon at 10 Downing Street, ostensibly to request a 20 minute interview for a front page profile piece on "Britain's First Lady" and "The Power Behind the Throne". As she explained to Tish Jones, it did not require her attendance as it only involved "hair, and clothes and nonsense." In reality, however, this was a ruse for Vivien to bring her findings on Harold Saxon to his wife. (TV: The Sound of Drums)

When Mickey shared the passwords to the UNIT website to the readers of his website in early 2006, he told them to "nose around" to find "hair-raising" truths about how the Slitheen weren't the first aliens mankind has met which UNIT had dealt with. (PROSE: )

Behind the scenes

 * Jon Pertwee adopted a bouffant hairstyle that grew larger with each season he was on Doctor Who. Writer Terrance Dicks claimed this was to hide a prevalent bald spot.
 * David Tennant wore a fake moustache to get genuine laughs from Billie Piper and Elisabeth Sladen.