By the late '80s, hip-hop was on its way to becoming a male-dominated art form, which is what made the emergence of Salt-n-Pepa so significant. As the first all-female rap crew (even their DJs were women) of importance, the group broke down a number of doors for women in hip-hop. They were also one of the first rap artists to cross over into the pop mainstream, laying the groundwork for the music's widespread acceptance in the early '90s.

Salt-n-Pepa were more pop-oriented than many of their contemporaries, since their songs were primarily party and love anthems, driven by big beats and interlaced with vaguely pro-feminist lyrics that seemed more powerful when delivered by the charismatic and sexy trio. While songs like "Push It" and "Shake Your Thang" made the group appear to be a one-hit pop group during the late '80s, Salt-n-Pepa defied expectations and became one of the few hip-hop artists to develop a long-term career. 

source: allmusic.com