Hairstyle Inertia

Hairstyle Inertia is the phenomenon where adult or teenage characters who Flash Back to a time in their childhood are frequently shown to have the exact same hairstyle, though those with long hair usually have shorter-- but not short-- hair. Pigtails, ponytails, braids, or other hairstyles that require long hair are also shown to be stubbier and shorter;is often used for Spinoff Babies.

It is not an Important Haircut-- those happen in series and are, as the title says, important to the plot. It is also not an Expository Hairstyle Change, which usually does not flashback to a character's childhood. This trope deals only with characters keeping the same hairstyle from childhood until the present time.

Additionally, this trope sometimes applies to some characters in a work of fiction, but not to others.

Similar to Same Clothes Different Year, only with hair.

And, barring the flashback, this may be Truth in Television, but just as likely is not.

Anime and Manga

 * Ichigo in Bleach.
 * Izaya, Shinra, and Kasuka in Durarara.
 * Shizuo (a natural brunette) is exempt from this list only because he dyes his hair blonde sometime around high school; the style itself is arguably the same since he was a kid.
 * Lelouch, Suzaku, Nunnally, Kallen, Euphemia, etc. in Code Geass.
 * Welkin, Isara, Alicia, Selvaria, and Maximilian from Valkyria Chronicles.
 * Mio, Ritsu, Yui, and Nodoka in K-On!.
 * Kyoya and Tamaki in Ouran High School Host Club.
 * Azuki and Mashiro from Bakuman｡.
 * Rei in Highschool of the Dead.
 * Urashima and Otsuu from Ookami San.
 * Rei I-III, Shinji, Asuka (substituting elastic bands for A10 Nerve Clips) and Misato from Neon Genesis Evangelion.
 * Kou/Ric and Nino from Arakawa Under the Bridge.
 * Shichika and Nanami from Katanagatari.
 * Rio, Kanata, and Filicia from So Ra No wo To.
 * Takaki and Akari in Five Centimeters Per Second.
 * Maya from Occult Academy (down to an identical dress...)
 * Everyone from Axis Powers Hetalia, except for the Double Subversion in the strip where England in the Middle Ages sees France's fashionably long hair and grows his out, only to have the style become unpopular. He plans on keeping it but lets France adjust it a bit. Instead France cuts it back to what it originally was, to England's chagrin.
 * Goku from Dragonball Z.
 * Justified: it has been stated that a Saiyan hair never changes from the day they were born.
 * Although this is only true with full-blooded Saiyans. Those who are only half like Gohan and Trunks will have hair that grows normally.
 * Chiyoko from Millennium Actress.
 * Hazumu and Tomari in Kashimashi Girl Meets Girl
 * All of the gang in Higurashi no Naku Koro Ni. Including Hanyuu though she is special since
 * Lucia in Venus Versus Virus.
 * Averted and played straight in Naruto.
 * Practically everyone besides Chouji, Lee, Tsunade, Sakura, Ino, Nagato and, Kushina.
 * Natsu, Gray, Juvia, Lucy, and, Jellal/Mystogan from Fairy Tail.
 * From the few flashback scenes so far, it looks like this applies to many of the main Star Driver characters--Sugata, Wako, Keito, Benio, George...
 * In the Magical Girl Lyrical Nanoha The Movie 1st Tribute Comics that doubled as promotions for the four manga running at the time of The Movie's release, the Lyrical Almanac had Subaru making up her version of how she and Teana first met, complete with child versions of the two that were still sporting their teenage hairstyles from StrikerS.
 * Wendy Garret of Gun X Sword has the same twin braids as a very young girl that she dons in series.
 * Played straight for most of the characters in Eyeshield 21. Especially noticeable in Sena, who has a serious case of Shonen Hair.
 * Hiruma, Musashi, Mamori, and Agon are aversions. Hiruma started dyeing and styling his hair in middle school, Musashi grew his hair out after becoming a construction worker, Mamori's had a few slight variations in her haircut, and Agon went through at least five different hairstyles in middle school alone.
 * Pretty much everyone in One Piece. A bit odd that many characters only recently chose to change their hairstyles all at once.
 * Subaru, Tasuku, Yoite, Kouichi, and Gau from Nabari no Ou.
 * Averted in Tenchi Muyo, where young Ayeka wears her hair in two pig tails instead of two pony tails. Given what we see of other Juraian princesses, this seems to be standard. Played straight with Ryoko.

Comic Books

 * Young Clark Kent/Superboy, in continuities where he exists, has the same hairstyle(s) as Adult Clark/ Superman (short, slicked back as Clark, spit-curl as hero). In continuities where Clark wasn't Superboy, Young Clark usually has the spit curl.

Film

 * Cloudy With a Chance of Meatballs starts with a scene of Flint as an 8-year-old, and he has the exact same Messy Hair that he does as an adult. Averted with Brent, who has a pageboy haircut as a kid,and a mullet as an adult.
 * Played with in Meet the Robinsons in that Wilbur has to hide Lewis's hair in order to keep his family from finding out that
 * Apparently Briony in the film version of Atonement wore exactly the same hairstyle from childhood until she was an old lady.
 * The Three Stooges in the 2012 film of the same name.

Live Action TV

 * Simon Tam, in the episode 5 flashback of Firefly.
 * Brian from Spaced has a flashback to his childhood, and he even has a goatee beard then. Mike also has a moustache in the flashbacks to the tree incident (and young Tim has bleached-blond hair as well).
 * Rose Tyler, from Doctor Who, has bleached-blonde hair, with noticeable brown eyebrows and roots. She was a natural blond when she was a small child.
 * Buffy the Vampire Slayer is shown as blonde as a child in a flashback to Dawn's (imagined) birth. It has previously been established that blonde is not her natural color. Fan Wild Mass Guessing has it that adding Dawn into continuity somehow changed her hair color.

Video Games

 * Larry, Edgeworth, and Phoenix in the first game of Ace Attorney have this.
 * More jarring is Maya. At the end of case 5 of Trials & Tribulations,
 * In the Disgaea Novels, Laharl has pretty much the same hairstyle when he was little, his antennae was just shorter.

Web Comics

 * Lisa of Penny and Aggie, visually distinctive for her hair dyed varying shades of red and tied into six pigtails, is shown having essentially the same hairstyle as a child, only with shorter pigtails.
 * Virtually all the non-adult characters of Homestuck are shown to have the exact same hairstyle throughout their entire lives.
 * We even see baby versions of all four kids and their guardians here, and their hair is exactly the same. Rose even has her hairband!

Western Animation

 * Marge Simpson already had her characteristic beehive as a toddler. Although apparently she wore her hair long and straight as a teenager, and then reverted to the beehive as an adult.
 * Bart and Lisa have the same hairstyles as babies as they do now. The future versions of all three kids have roughly the same hairstyles as well.
 * As a baby, Homer had two hairs on his head, similar to what he has now. Though he did have a full head of hair between childhood and Marge's first pregnancy.
 * Averted as a Running Gag with Dr Hibbert - every time he's appeared in a flashback, he's had a different haircut, usually one that's associated with the time period in question.
 * Katara and Sokka from Avatar: The Last Airbender both had the same hairstyle when they were single-digit aged as they do now that they're teenagers. The same is true for Azula, but not for Zuko.
 * While similar, in "The Southern Raiders" you can see notable if small differences in their childhood hairstyles. However, during Katara's opening speech in the first episode which takes place two years before the start of the series, their hair is identical to the present day.
 * In The Legend of Korra, Katara's hairstyle remains nearly the same 70 years later when she's Avatar Korra's Waterbending master, complete with hair-loopies.
 * Johnny Bravo had his trademark hair and sunglasses as a small baby in the crib... as well as his trademark libido.
 * Dib and Gaz from Invader Zim during flashbacks.
 * Brock Samson of The Venture Brothers animated TV show seems to have had his trademark mullet for a long time, even back when he was in college during an episode where team Venture and pals are taken hostage by a supposedly dead college room-mate.
 * Phineas and Ferb has a lot of these. The most exaggerated example is Linda Flynn, since she had the same hairstyle when she was a baby.
 * The American Dad animators always try to incorporate Hayley's headband into scenes where she is younger.
 * Also in one episode we flashback to Steve and his friends at the age of four, in a montage we see them growing up together, never changing there hairstyle.
 * The main six kids in Recess when they were toddlers.
 * Averted and parodied in Futurama when a flashback of Zoidberg shows him to have had hair. Amy asks in shock, "Zoidberg had hair?!" to which Farnsworth says that he didn't and that if Amy imagined him that way, that's her business. It's then revealed that fear causes Zoidberg to grow hair, and he really did used to have it, and has it again by episode's end (only to not have it anymore at the start of the next).