Suppressed Mammaries

A popular, often young, female TV star is fairly flat-chested, or at least not very "pronounced", in her most recent or well-known role... but then you see her in an awards show or otherwise live event, and my, has she grown.

This Trope only applies to cases wherein the titular mammaries were quite obviously suppressed for the sake of the role, and so if the actress underwent breast-oriented plastic surgery or a reasonable length of "developing time" had passed between the role and her more recent appearance, it is not an example of this trope (though this trope does give the tabloids plenty of "Did she get a boob job?" fodder).

Often a result of Not Allowed to Grow Up. Compare/contrast Big Bra to Fill, where the character has a big bust but the actress doesn't.

Disney

 * Done in Mulan by the titular heroine to hide her true gender because women were not allowed in Ancient China's military. She only gets found out after already proving her worth, which becomes a plot point later due to the earned trust of her comrades.

Film
"Toddy: Now we've had two major obstacles to overcome... Victoria: [sobbing] My bosom... Toddy: First, to convince everyone that you're a man... Victoria: It's been damned uncomfortable. Toddy: What has? Victoria: Strapping down my bosom. Toddy: Now all you have to do is go out there, and you'll be a star for the next twenty years. Victoria: Toddy, if I have to strap down my bosom for the next twenty years they're going to look like two empty wallets."
 * This was famously done to Judy Garland to make her look younger for the role of Dorothy Gale in The Wizard of Oz.
 * Rumors of this being done deliberately in Star Wars are false. True, Carrie Fisher's breasts were taped down to prevent Gainaxing under her costume, but she resorted to that expedient herself after George Lucas told her that women couldn't wear bras in space! Lucas eventually got the Hotter and Sexier he originally wanted with the notorious "metal bikini" slavegirl outfit in Return of the Jedi. Fisher went on to relate the whole sordid affair in her candid (and screamingly funny) memoir Wishful Drinking
 * Christina Ricci tied her breasts down when she played Wednesday Addams in the movie version of The Addams Family and Addams Family Values. Puberty did not miss her. In what was almost assuredly a reference to this fact, her opening scene of Now And Then has her duct-taping her bra.
 * This happened to Evanna Lynch in the fifth and sixth Harry Potter movies. While not overly endowed compared to other young actresses her age, she is noticeably bustier than her other female castmates.
 * Emma Watson is reported to have resorted to binding herself during some of the later Harry Potter movies, due to "growing up" faster than her character.
 * A strange in-universe example in Orphan, which has Leena Klammer put cloths and bandages around her breasts to look more childlike.
 * In The Railway Children (1970), one of the female leads (I believe it was Jenny Agutter) had to have her breasts strapped down because she was playing a much younger girl. In fact, this was such a big secret at the time that she wasn't allowed to smoke or drink off the set during filming, or for quite a while after that to keep up the pretense.
 * A rare adult example: Julie Andrews did this in Thoroughly Modern Millie in order to achieve The Roaring Twenties-appropriate Pettanko "flapper" look and Lampshaded it within the Film.
 * A second Julie Andrews example is Victor Victoria: Victoria (and consequently Andrews) was forced to bind her breasts in order to disguise herself as the "female impersonator" Victor. Once again it's Lampshaded when Victoria complains about the discomfort and expresses a fear that she's damaging her figure.
 * The exchange in it's entirety for your amusement:


 * Tami Erin for her role in "The New Adventures of Pippi Longstocking" (1988). It became obvious during a Nickelodeon interview promoting the movie when she wore a tight aerobics leotard without the binding.
 * In a rare non-age-related example, Lindsey Lohan's bust was digitally reduced for Herbie Fully Loaded to avoid 'offending' audiences.
 * Selena Gomez in Ramona And Beezus. While not bigger than the average teen actress her age, then 17-year-old Selena's bust was a bit too big for the 15-year old she was playing and wore bras that made it look smaller.

Literature

 * Delfina in Diane Stuckart's Leonardo da Vinci mysteries is a Sweet Polly Oliver who binds her breasts and apprentices herself to Leonardo under the name "Dino". She goes to great lengths to conceal her bandages.
 * Alanna in the Song Of The Lioness quartet, as part of her disguise. She starts out using bandages, but eventually gets a special corset.

Live-Action TV

 * Jennette McCurdy from iCarly. In between Season 1 and 2, the actor who played Freddie grew up.. and Jennette grew outward. Since then, the show has taken to wrapping Sam up in layers of 3 or 4 t-shirts, but she's kept on growing. A few episodes in season 3 they forgot about this, such as the rabbi scene in iSaved Your Life, and it's pretty obvious what they are doing.
 * Julianna Rose Mauriello had to have her breasts taped down since puberty on LazyTown since Stephanie is supposed to be 8 years old (or 9 now, since one year's passing has been acknowledged). She was 17 during the last episodes she filmed, and has since been replaced by another, much younger, actress.
 * That said, 'Stephanie' (Solla Stirða) was played by actual adult women in all the original Icelandic plays from before the TV show, and one of them was quite busty with no attempt to do anything about it; while Julianna definitely had grown between seasons and doesn't really look any bigger in out-of-character shots from the same era.
 * Annette Funicello and the other female Mouseketeers, supposedly at Walt Disney's personal insistence.
 * Buffy in later seasons of Family Affair. It did not end well for Anissa Jones, her actress.
 * On Small Wonder, the plastic vest Tiffany Brissette wore to simulate Vicki's access panel had to be periodically refitted over the show's four-year run. In the fourth-season episode "Double Dates", Brissette shows us how uncomfortably tight her wardrobe had become.
 * Soleil Moon Frye discussed this in an interview on a Canadian talk show for teens only a couple of months after Punky Brewster was canceled. She suffered from gigantomastia and later underwent a breast reduction.
 * Jordan Todosey in Degrassi, where she's playing a transboy; Adam's shown binding (with an Ace bandage) onscreen. Later it's mentioned in-series that Adam gets a chest compression vest.
 * Played with in Skins when Sketch binds down her breasts to try and be more appealing to Maxxie, who is gay.
 * Referenced in Frasier wherein Daphne reveals she was once on a popular television show in England and "Of course, by the end of the series, I was sixteen, five foot ten, and they had me boozies bound up tighter than a mummy."

Other

 * The Flapper era of The Roaring Twenties: Slim was in, and every rebellious flapper girl suppressed her breasts as much as she could possibly get away with.
 * There was even a company called Boyishform that made bras just for this reason; Maidenform was so named as a Take That to the whole craze.
 * Patty Maloney once wrote that she had her chest bound whenever she portrayed a little girl.
 * When older cast members of the musical version of Annie would start to develop, many did this in order to avoid being fired from their roles.
 * It is speculated that in The Legend of Zelda: Ocarina of Time.

Webcomics

 * Natani from Twokinds is quite literally a man's soul trapped in a female body, so "he" uses this trope to keep "his" physical gender a secret.
 * Yuki of Sparkling Generation Valkyrie Yuuki tried to do this, but ended up passing out due to her inability to breathe. Being a victim of Gender Bender and all that.
 * Tai from Questionable Content mentioned that she did this at one point to pass as a boy; she kept it up later just for a pretense of androgyny.
 * Megatokyo's resident cute robot girl Ping did this at one point in an attempt to return to her "plain" appearance. Upon learning the truth, Junko Ibara berates her for doing this, saying, "It's not good for them!"

Real Life

 * Transmen and Drag Kings are often required to do this in order to pass, unless, of course, they have the body of a Pettanko naturally. It is anywhere from slightly to very uncomfortable, depending on the size of their breasts and the method used to flatten them out.
 * Also a common practice for women playing male characters in stage productions.
 * Sometimes, female cosplayers dressed as male characters - called crossplayers - will practice this to look more convincing as males. The end result would be a Bifauxnen quite often. Utilizing Sarashi to achieve this is fairly common.
 * Proper fit for a traditionally draped woman's kimono often calls for the help of Ace bandages or Sarashi. Pre-war Japanese fashion favored a Grecian column build that often required waist padding, chest binding, and a hip girdle to achieve, even at the time. Women today are (on average) substantially heavier and curvier...and proper fit is accordingly even more difficult to achieve.
 * Before women were allowed to serve in military forces, they did this and tried to pass it off as being young men (because the beard thing tends to be an issue when trying to pass off as an adult male) and thus serve. An effective technique would be to use of a decoy of pretending to be too young to serve, and have someone figure that out, and then think they knew your secret. This charade tended to end if the woman in question was injured, because almost inevitably either their pants or shirt would have to come off...
 * Jessica Simpson began her career in show business as a Christian pop singer. During this stage of her career she would often tape down her breasts for performances because her promoters felt that an attractive blonde with D-cup boobs wasn't the best image for a gospel singer.