BOL4 is the shortened rebranding of Bolbbalgan4 (볼빨간사춘기), is the solo project of Ahn Ji Young (안지영; born September 14, 1995), formerly a two-member indie female duo (composed of Ahn Ji Young and Woo Ji Yoon) formed by Shofar Music. They participated on Superstar K 6 in 2014 and signed a contract with their current company, but didn't make their debut until 2016. They officially debuted with the mini album RED ICKLE on April 22, 2016.

As of April 2, 2020, Shofar Music has announced that Bolbbalgan4 will be shifting to a one-member lineup as Woo Ji Yoon left the group. Ahn Ji Young will be continuing as a soloist under the group's name. Read more on Last.fm. User-contributed text is available under the Creative Commons By-SA License; additional terms may apply.