BOL4 is a shortened rebranding of Bolbbalgan4 (볼빨간사춘기). Bolbbalgan4 is an indie female duo (Ahn Ji Young & 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 sets to leave the group.