We present reflection high energy electron diffraction, secondary ion mass spectroscopy, scanning tunneling microscopy and x-ray photoelectron spectroscopy studies of the abruptness of InAs-GaSb interfaces. We find that the interface abruptness depends on growth order : InAs grown on GaSb is extended, while GaSb grown on InAs is more abrupt. We first present observations of the interfacial asymmetry, including measurements of band alignments as a function of growth order. We then examine more detailed studies of the InAs-GaSb interface to determine the mechanisms causing the extended interface. Our results show that Sb incorporation into the InAs overlayer and As exchange for Sb in the GaSb underlayer are the most likely causes of the interfacial asymmetry.