In both fiction and reality, gradual hair loss isn't considered especially serious. Generally speaking, it's a sign of either aging or going Prematurely Bald, and treated as embarrassing, funny, or just depressing.
And then there are occasions when a character's hair loss is unexpected, in large amounts at once, or progresses quickly as a sign of something much more worrying, tragic, or even horrifying. Maybe it's the prelude to a potentially fatal illness, a hint of radiation exposure, the first sign of a monstrous Slow Transformation, chronic stress, the effects of chemotherapy — the list goes on and on. One way or the other, the character's loss of hair is a symptom of something very bad.
Expect at least one scene where the hair can be seen shedding away in the character's hand, or where a huge clump of hair is found on a comb.
A possible example of Virus Victim Symptoms or even a future Bald of Evil. Compare Traumatic Haircut and Important Haircut; contrast Hair Today, Gone Tomorrow. See Deadly Nosebleed and Incurable Cough of Death for other possible early warning signs of death or worse.
- Demon Slayer: Kimetsu no Yaiba: While in Mount Natagumo, Zenitsu is bitten by a spider and encounters several grotesque, spider creatures. He is greeted by the Older Brother spider demon who informs him that he will be gradually turned into one of the spider creatures and describes the process. As they fight, Zenitsu finds his hair is falling out and yells that he was never told about that aspect of the transformation.
- During the Chimera Ant Arc of Hunter × Hunter, Knov's hair turns completely white after he has a breakdown from coming into contact with Shaiapouf's powerful En. His breakdown is so severe that he is unable to carry on with the assault on the palace, and when he is seen, he has lost almost all his hair and is in a deeply depressive state. By the end of the arc, he has completely lost his hair, and wears a hat to hide his head.
- The Big Finish Doctor Who audio drama "Protect And Survive" features Ace and Hex getting trapped in a parallel world where the Cold War gives way to World War III and only just managing to escape the bombardment in a makeshift fallout shelter owned by Albert and Peggy Marsden - though not before Hex is blinded by the blast. Unfortunately, it soon becomes clear that the shelter wasn't enough to keep out the radiation: Ace admits to Hex that she found a lot of hair on her pillow that morning, gloomily remarking that "the skinhead look" doesn't suit her. Fortunately, time rewinds itself not long afterwards; unfortunately, it turns out the Marsdens are trapped in a "Groundhog Day" Loop into which Ace and Hex have now been incorporated.
- When the Wind Blows features Jim and Hilda gradually succumbing to radiation sickness in the aftermath of a global thermonuclear war. By day five, Hilda's hair is coming out in clumps, and because both of them are completely oblivious (or in denial) as to how doomed they are, Jim tries to reassure her by telling her that "women don't go bald." Shortly after this, both of them stagger back into their inner refuge, don paper bags, and quietly expire.
- Chocolate: In this touching foreign film, an autistic girl named Zen always found solace growing up by petting her mother's hair. The severity of her mother's cancer is made clear to her when she learns her mother is now wearing a wig and her hair has been falling out as a result of the chemotherapy, prompting Zen to do what she can to pay for her mother's treatment... which is kicking people until they give her money.
- The Day After, being set before, during and after a nuclear war between the United States and the Soviet Union, naturally features several characters losing clumps of hair as radiation exposure takes its toll on them. In one especially poignant scene, Denise Dahlberg laments that the makeshift hospital she's staying at has given her a ribbon - only by now, she doesn't have any hair to put it in. Doubly tragically, the ribbon is actually a color-coded sign that the patient is going to die and should not be given any further medical attention.
- In Fantastic Four (2005), not long after getting zapped with cosmic rays alongside the future superhero team, Victor Von Doom begins losing strands of his hair - the prelude to a transformation into a metallic monster.
- As Seth Brundle's body horroriffic mutation progresses in The Fly (1986), he begins shedding hair - along with fingernails, teeth and genitals. By the time Veronica arrives at the lab to say goodbye to him and reveal that she's pregnant with his child, Seth's hair has been reduced to a few stray lengths of hair across his misshapen skull.
- In the HBO movie Gia, the titular model's hair loss due to complications of AIDS which she succumbs to is obvious towards the last hour of the film.
- The 1995 remake of A Little Princess features Lavinia being "cursed" by Sara in response to her mistreatment. While obsessively brushing her hair later that evening, Lavinia finds a large strand of hair coming out along with the brush, prompting her to faint in shock.
- Emily from The Ultimate Gift. Initially an excitable and optimistic girl, she develops cancer where during her last moments, she's lost her hair and looks frail, a depressing parallel to what she used to look like
- X-Men: Apocalypse features Charles Xavier finally going bald as a result of psychic trauma inflicted by Apocalypse.
- In The Bridge of Clay Penny Dunbar is dying of cancer and undergoing chemo. She starts losing her beautiful blonde hair and in a very poignant scene asks her husband and five sons to cut it very short, because she can't stand losing whole strands of it.
- In The Midnight Gang, Sally has an ambiguous, serious illness that acts like cancer, including she's bald and it's said to be from the treatment.
- Subverted in Necroscope; Russian necromancer Boris Dragonani begins exhibiting a receding hairline around the halfway point of the book, and his boss attributes this to poor health. In the narration, however Boris reveals that his hairline isn't receding at all: his skull is changing shape. As it turns out, he's been infested with a wamphyri symbiote and he's transforming into a vampire.
- The Pale Horse: All of the victims of the "witches" had hair loss as one of their symptoms. Mark Easterbrook deduces that this implies that they all died from Thallium poisoning.
- Red Dwarf: Infinity Welcomes Careful Drivers features a brief aside that first introduces the concept of Game Heads: basically anyone suckered in by the highly-addictive inescapable VR game "Better Than Life," the Game Head encountered has been addicted for so long that her once-long hair has been reduced to "a series of greasy whips," presumably as a result of malnutrition.
- In Sister Pelagia and the Black Monk, the monks inhabiting a holy island hermitage see hair loss as a mark of God's approval and, indeed, often pass away quickly after it sets in. This is because the island hosts a highly radioactive meteorite, and the monks are actually dying of radiation poisoning — in the end, even the Big Bad (who has been hiding out on the island for half the book) starts losing hair, indicating that he may not live long, even if he escapes from justice.
- In Wolves Eat Dogs, a sequel to Gorky Park that takes place in the Chernobyl Exclusion Zone, Renko pointedly asks one resident how much of his hair comes out whenever he combs it.
- After finally being talked into undergoing chemotherapy for his lung cancer, Walter White of Breaking Bad begins losing clumps of hair. Though Jesse offers some helpful advice to avoid hair loss, Walter ultimately shaves his head completely bald, creating his signature look and paving the way for his transformation into Heisenberg.
- Experienced by Professor Legasov in the final episode of Chernobyl; by this stage, he already knows that he's been exposed to enough radiation to guarantee cancer within a few years of the disaster, but finding a clump of hair in his hand confirms that he's running out of time.
- Mr Halpen, head of Ood Operations in the Doctor Who episode "Planet Of The Ood." Throughout the episode he's in, he loses a lot of hair - which is revealed to be due to the Ood graft in his drink and eventually turns him into one of the Ood.
- Following his fall into a vat of toxic chemicals, Jeremiah Valeska of Gotham emerges horribly scarred and poisoned; by the time we see him again, he's left with only a few strands of hair on his head.
- One early episode of Misfits features Kelly suddenly and dramatically losing all her hair in the shower; after being given a clean bill of health by a doctor, she's sent back to community service with her bald dome hidden by a wig and baseball cap. It turns out she's under the influence of another superpowered young offender, this one with the ridiculously lame power of cursing people with alopecia.
- Murdoch Mysteries: The culprit of "The Ghost of Queen's Park" begins losing her hair in the final scene she appears in, a side effect of the radium dust she painted herself with in order to appear ghost-like.note
- NCIS episode "Dead Man Walking" began with a man arriving at NCIS headquarters to report his own murder, shedding a clump of hair in his hands as he does so; turns out he's been poisoned with thalium-laced cigars. Despite being given immediate medical care, he's been exposed too long to recover, and dies shortly after the episode's end.
- Queen Sugar: Violet's hairdresser becomes concerned when she notices that Violet's hair is falling out and recommends that she go to a doctor. When she does, Violet gets diagnosed with lupus. Justified because hair loss is one of the many symptoms of lupus.
- Two and a Half Men: After realizing they're short on money, Alan signs up for an experimental drug trial for which he'll be handsomely compensated. Later that day, a chunk of his hair falls out, leading him to conclude that he "isn't in the control group".
- Star Trek:
- Characters tend to lose hair when they're assimilated by the Borg, their hair follicles presumably being killed off by the nanites injected into their bodies; ironically, the first victim of this process was the famously-bald Captain Picard.
- In the Star Trek: Voyager episode "Threshold," Tom Paris mutates and dies following an escapade too ridiculous to explain; however, he awakens right before the autopsy is due to begin, and immediately finds himself visibly shedding clumps of hair as a sign that his mutation is continuing. He ends up turning into a giant salamander, inflicting the same process on Janeway, mating with her, and producing a litter of children before the transformation can be reversed. No, really.
- In the Voyager episode "Scientific Method," a group of invisible aliens begin performing a number of weird experiments on the crew, resulting in catastrophic injuries, illnesses and mutations. In Chatokay's case, they subject him to Rapid Aging - and of course, the first hint that something's wrong is a scene where his hair starts falling out in clumps.
- In The Strain (TV series), Eph and Alex investigate an abandoned town and encounter a woman who claims that the Strigoi have set up a prison camp nearby. She says she escaped from there, but then pulls out a lock of her hair, revealing that she's been infected and is turning into a Strigoi herself.
- The Nosferatu clan of Vampire: The Masquerade are almost invariably bald on top of being hideously disfigured, the result of a week-long metamorphosis during which newly-Embraced Nosferatu vampires are warped beyond recognition: during days two to four, while the cartilage of their nose and ears begins to distort, their hair begins to fall out in patches - usually revealing more disfigurations of the skull in the process.
- Hair loss is usually part and parcel of transformation into a ghoul, though to varying extents: some ghouls are completely bald, while others have only mild cases of alopecia, and occasionally it's possible to meet a ghoul with a full head of hair.
- Despite the deliberate inaccuracies featured throughout the games, the series occasionally likes to incorporate some of the real-world results of radiation exposure - including hair loss. In one morbidly amusing case, this led to a man believing that exposure to radiation was transforming him into an immortal ghoul after he found himself losing clumps of hair, when in reality he was just dying of radiation sickness.
- Subverted in Fallout: New Vegas with Chris Haversam, a human from Vault 34 who has joined the all-ghoul Bright Brotherhood religious group. Chris believes himself to be a ghoul because, as Vault 34's reactor technician, he was exposed to a large amount of radiation, he speaks with a gravelly voice (a trait many ghouls share), and eventually his hair began to fall out. The last part was in all actuality, just male pattern baldness setting in. Ironically, Vault 34's reactor malfunctioned after he left and turned most of the other dwellers into ghouls.
- One episode of Best Ed has Buddy dealing with fur loss. At first, both he and the doctor think it's from stress and it'll stop falling only if he starts being more positive. At first, this appears to be the case, since Ed constantly does something stupid that annoys him, and patches of fur fall any time this happens. His fur grows back in the morning after he realizes a life without Ed is worse than a life without fur. However, it turns out the reason his fur was falling was because Ed was using his personal comb to clean the toilet.
- Happens to Nancy Gribble in the King of the Hill episode "Hair Today, Gone Tomorrow" due to stress over her lingering feelings for John Redcorn. She finds out from her mother that this is actually a common trait for the women in her family, as the elder Mrs. Hicks has been wearing a wig for some years. While Nancy tries to save her looks by rekindling her relationship with Redcorn, she ultimately chooses to stay faithful(ish) to Dale and resolves to also wear a wig when the time comes.
- The Simpsons episode "Simpsoncalifragilisticexpiala(Annoyed Grunt)cious" features Marge beginning to lose her hair due to the stress she's under in dealing with her family's shenanigans.
- In Total Drama Revenge Of The Island, Staci instantly becomes bald after she receives the toxic mushroom (which is radioactive) after she's eliminated. Likewize, Dakota becomes bald after getting exposed to radioactive waste. However, it doesn't last long in her case, since the real consequences of the radiation manifest when she mutates into a monster (her hair grows back, but is green and spiky instead of the long blonde hair she used to have).
- One of the many signs of radiation exposure is hair loss, whether accidental or part of therapy.
- Thalium poisoning, on top of being incredibly painful, also results in hair loss.
- Hair loss can be a symptom of several diseases and disorders, including those involving hormones (particularly the thyroid) or autoimmune problems.