Even though breasts existed long before this year, 2015 was a time of immense social pressure to change the way we look and talk about them. With Free the Nipple aiming to fight the sexist treatment of female nipples, countless online movements to normalize breastfeeding, and a lot of celebrity support for both of these things, 2015 was the year of the breast.

Here are some memorable moments from 2015 that worked to challenge societal treatment of breasts.

1. #FreetheNipple had its moment.

Though the #FreetheNipple movement started prior to 2015, it gained a lot of leverage and attention on social media this year. Under the #FreetheNipple social media campaign, both men and women have called out Instagram's nipple policy, which has a double-standard against female nipples. Earlier this year, ATTN: interviewed Los Angeles-based startup advisor James Shamsi, who conducted a social experiment on Instagram to highlight the absurdity of the social app's nipple rule.

Shamsi posted a zoomed in Instagram photo of a male chest that resembled female breasts and asked his Facebook friends to report the image as inappropriate to Instagram. Instagram then removed the photo, but when Shamsi told the company that it was actually a picture of a male chest, the photo later reappeared on his account.

RELATED: This Guy Just Challenged Instagram's Nipple Policy in a Very Clever Way

"UPDATE: Instagram reinstated the photo because these were male #facepalm," Shamsi wrote on Instagram.

Shamsi, who also made the app #KardBlock to keep Kardashian news out of one's social media feeds, previously told ATTN: that his goal was to expose gender inequality in the social media space.

"I believe in fighting for equality wherever and whenever possible ... from creating #KardBlock to make the internet fairer in getting real news out there instead of Kardashian news all the time to help fighting nipple inequality."

RELATED: Women Are Fighting Sexist Double Standards on Social Media

Several months ago, Instagram CEO Kevin Systrom explained that there's a business reason for Instagram's strict nipple policy. At an event hosted by Dazed Media, he said Apple has tight rules for apps and that violating any of these guidelines could result in Apple getting rid of the Instagram app. Apple only allows explicit nudity in apps if the app is for users that are 17 and older, and because Instagram is popular among young kids and listed for people ages 12 and over, Instagram had to make some "tough calls" in order to "scale effectively" as an international business.

Systrom also said that there are lots of other places online to find female nipples, but as ATTN: previously noted, the #FreetheNipple movement was never about promoting nudity on Instagram. It's about showing that we treat female nipples differently than male nipples.

2. Women took a stand to normalize breast-feeding on social media.

Social media can pose challenges for mothers trying to share their breast-feeding moments with friends. Over the summer, birth photographer Melissa Jean Wilbraham was temporarily banned from Instagram for posting photos of breast-feeding women and women giving birth.

When Wilbraham tried to log in she saw the following message:

"Your account has been deleted for not following our terms. We’re unable to restore accounts that are deleted for these types of violations."

After she took to Facebook to complain.

"How ironic that the very day 'World Breastfeeding Week' began, my business was removed from Instagram," she wrote at the time. "There will always be sad humans who report my images but I will NEVER let this stop me celebrating & normalizing the miracle of life heart emoticon #‎bringbackmelissajeanbabies #‎bringbackmelissajean."

Instagram went on to reactivate her account, and the company told the Daily Mail Australia in a statement that deleting it was a mistake. Though Wilbraham received a lot of support for her work following the incident, she said in a separate interview that getting banned could have hurt her business because Instagram is such a big part of her brand. At present, she has nearly 58,000 followers.

Even though 49 states plus the District of Columbia and the Virgin Islands allow women to breast-feed in public, many women both in and outside the U.S. still face shame for nursing their children in restaurants and other public places. In November, Florida mom Ashley Kaidel gained a lot of attention online after writing a viral Facebook post about a woman glaring at her as she breast-fed her child in a restaurant.

Kaidel wrote:

"She is looking at me with disgust and shaking her head with [judgment] in an attempt to shame me and indirectly tell me without words that I am wrong and need to cover myself. [T]he reason I post these types pictures is for the mother that tried breastfeeding uncovered once and she got shamed, she got stared and pointed at, she got nasty comments, she got asked to leave the room, she got asked to cover up."

RELATED: Fighting Society's Ridiculous Breastfeeding Stigma

Kaidel added that it is hypocritical of people to celebrate breasts in sexy ads yet take offense when women use their breasts to feed their children. The popular meme below runs this point home:

David Wolfe Facebook - facebook.com

Earlier in 2015, YouTube star Kristina Kuzmic illustrated the absurdity of anti-breast-feeding logic in her satirical viral video titled, "4 Reasons Women Should NEVER Breastfeed in Public."

"We don't live in a society where it's OK to just show part of your breast and cleavage in public," Kuzmic says before showing footage of a woman breast-feeding her baby right next to an ad of a woman posing in underwear:

Kristina Kuzmic YouTube - youtube.com

You can learn more about the growing movement to normalize breast-feeding in this ATTN: video: 

RELATED: WHAT HAPPENED WHEN A PHOTOGRAPHER PUT BREASTFEEDING PHOTOS ON INSTAGRAM

3. Celebrity visibility

In 2015, many celebrities came forward in support of #FreetheNipple and the normalization of breasts on social media. Singer Miley Cyrus has been a longtime supporter of the message behind #FreetheNipple and has posted photos of her breasts on Instagram before. Wearing pasties to a summer interview on "Jimmy Kimmel Live," she said it's crazy that so many people are uncomfortable with nipples even though every person has these body parts.

"Humans aren't afraid of the human breast. It's the nipple that's the issue ... I'm showing my boobs and no one has a problem because the nipples are covered so somehow that's OK. America's actually fine with tits. It's nipples they don't like... The nipple, you can't show, everyone has, but the jug part that everyone doesn't, you're allowed to show under-boob."

You can see the full, hilarious interview here:

In 2014, she posted a topless photo of herself on Instagram with the caption, "Some lame a** deff gonna (flag) dat (s***) but f********k it #practicewhatchupreach #FreeTheNipple #freedats***." Instagram deleted the image.

RELATED: The Problem with the Way We Talk About Breastfeeding

Cyrus went on to post other subtle photos of her nipple on Instagram:

Model Chrissy Teigen, a star social media user, has also gotten behind #FreetheNipple. This year, Instagram removed one of her topless W magazine photoshoot images, and she responded by posting this photo that hides the sight of her nipple but still reveals much of her breast:

Teigen then mocked Instagram by posting a photo of husband John Legend's butt. The platform did not remove that photo.

"The fact that I have to censor myself from my photo at all when there are full-on porn being shot across Twitter and Instagram every day is crazy," Teigen told Mashable in an interview. "But women are beautiful and if it's a beautiful photo that isn't vulgar, then who cares?"

Though actress Alyssa Milano is uncertain about the effectiveness of #FreetheNipple, Milano herself has been a staunch advocate for the normalization of breast-feeding on social media. Milano has repeatedly confronted society's taboo around breast-feeding in public, arguing that women shouldn't have to feel bad about feeding their children because some people are bothered by breasts.

RELATED: Alyssa Milano's Halloween Costume Had A Great Feminist Message

Milano recently shared a powerful photo of herself breast-feeding her one-year-old child, Elizabella, writing that it has been "one of the greatest joys in my life to breastfeed my babies." Milano's post received nearly 35,000 likes on Instagram and more than 140,000 on Facebook, with many commenters applauding her tireless efforts to normalize breast-feeding.

When Elizabella turned one in September, Milano got a lot of flak on social media after posting a photo of herself breastfeeding the child as a newborn.

"I think people are more comfortable sexualizing breasts than relating them to what they were made for, which is feeding another human," Milano told Entertainment Tonight in September.

During Halloween, Milano made news for posting a #TBT photo of herself as Wonder Woman breastfeeding her child.

"Normalizing breastfeeding will be a lot more effective in advancing women’s issues and desexualizing breasts," Milano wrote in a September TIME article. "Yes, they’re pretty. And yes, they have a purpose in women’s sexuality. But their main purpose is to feed another human."

RELATED: People Are Loving Alyssa Milano's Daring Breastfeeding Post