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Constance Wu says she loves her daughter's 'blue butt' — here's what that is

The "Crazy Rich Asians" star discussed her nine-month-old daughter during a rare public moment on "The Tonight Show Starring Jimmy Fallon."
/ Source: TODAY

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Constance Wu’s daughter has a case of the… blue butt?

During her appearance on “The Tonight Show Starring Jimmy Fallon” on Friday, Wu, 39, gushed about her nine-month-old daughter in a rare moment to Jimmy Fallon, including one of her more curious features.

When Fallon asked the “Crazy Rich Asians” star how her daughter was doing, Wu immediately responded, “She’s the best! She has a full head of hair, she has a blue butt.”

The 46-year-old host tried to slide past the piece of information Wu dropped, pivoting to a question about whether or not she or the baby were getting any sleep. Wu interrupted Fallon’s question, fake-yelling at him, “You didn’t ask me about the blue butt, Jimmy! I thought that you might be curious about the baby with the blue butt.”

Fallon admitted that he didn’t understand what Wu had said and decided to skip past it. He played along with Wu’s story, inquiring about the aforementioned blue butt.

“Yes, her butt is the color blue,” Wu said. “There’s this thing, I had never heard of it before, but it’s called a ‘Mongolian spot.’ And apparently, it happens in a lot of Asian babies, and my boyfriend and I are both Asian, and it’s where your butt is blue for the first two years of your life and then it just goes away.” (The medical community is steering away from the phrase "Mongolian spot," which is a dated and racist term.)

Constance Wu on Oct. 9, 2018 in Los Angeles, California.Axelle/Bauer-Griffin / FilmMagic

Fallon was still unsure if Wu was doing a bit, asking the audience in the studio if they had ever heard of a "blue butt" before. Lucky for Wu, an audience member had it themselves as a baby, validating her story.

“It’s a very special thing and it’s not something that she gets to show off while she’s walking down the street, not that she’s walking yet,” Wu joked.

Fallon later asked Wu if her boyfriend, frontman for the band Man Man, Ryan Kattner, played music to their baby, to which Wu replied, “He actually wrote a song about her blue butt, so that will be on his next album.”

What is blue butt?

According to the Mount Sinai Health System, congenital dermal melanocytosis (previously known as Mongolian spots) are a type of flat birthmark that is typically blue or blue-gray. The color is from a collection of melanocytes — the cells that make skin pigment — that form within the deeper layers of a baby’s skin.

As Wu mentioned, they are common among children of Asian, Native American, Hispanic, East Indian, as well as African descent. Luckily, they aren’t cancerous or associated with any specific disease and require no tests or treatments as they are normal birthmarks that will naturally fade within a few years.

Some fans took to the comments section of the YouTube clip with their own theories on what a "blue butt" is.

"Blue butt is common birth mark for baby," one person wrote. 'There’s a story about the blue butt. If the baby is not willing to be born to earth, the goddess os birth will tap the baby and push the baby."

Another fan added, "In my culture, the superstitious of a blue butt means in the baby's past life, his/her/their was a mischief/prankster."

Wu’s cute story on “The Tonight Show” was the first public update she’s provided on her daughter since news broke last December that she had given birth to her first child over the summer, as her social media accounts are now “defunct.” Both Wu and Kattner, who goes by the stage name Honus Honus, have remained largely private about their daughter since she was born.