A nasal cannula comprising: a securement system for the nasal cannula, and a tube connected to the nasal cannula providing at least a part of a breathing circuit for a user of the nasal cannula, and wherein the securement system comprises a two-part releasable attachment arrangement, the arrangement comprising: a dermal patch (550, 2008) and a user interface patch (552, 2007), the dermal patch (550, 2008) comprising a patient side and an interface side, the patient side of the dermal patch (550, 2008) configured to attach to the skin of a user, the interface side of the dermal patch (550, 2008) comprising a first part of the two-part releasable attachment arrangement, and the user interface patch (552, 2007) comprising an interface side and patient side, the patient side of the user interface patch (552, 2007) comprising a second part of the two-part releasable attachment arrangement, the second part being complementary to the first part, the interface side of the user interface patch (552, 2007) being attachable to the nasal cannula, and wherein the nasal cannula comprises: at least one nasal prong, each said prong having a gas outlet adapted to be inserted into a user's nare and a gas inlet fluidly connected to the gas outlet, the at least one nasal prong comprising a backing, the backing configured to rest on a user's face, wherein a lip extends about at least a part of the perimeter of a rear surface of the backing, the rear surface configured for receiving or retaining the user interface patch. a securement system for the nasal cannula, and a tube connected to the nasal cannula providing at least a part of a breathing circuit for a user of the nasal cannula, and wherein the securement system comprises a two-part releasable attachment arrangement, the arrangement comprising: a dermal patch (550, 2008) and a user interface patch (552, 2007), the dermal patch (550, 2008) comprising a patient side and an interface side, the patient side of the dermal patch (550, 2008) configured to attach to the skin of a user, the interface side of the dermal patch (550, 2008) comprising a first part of the two-part releasable attachment arrangement, and the user interface patch (552, 2007) comprising an interface side and patient side, the patient side of the user interface patch (552, 2007) comprising a second part of the two-part releasable attachment arrangement, the second part being complementary to the first part, the interface side of the user interface patch (552, 2007) being attachable to the nasal cannula, a dermal patch (550, 2008) and a user interface patch (552, 2007), the dermal patch (550, 2008) comprising a patient side and an interface side, the patient side of the dermal patch (550, 2008) configured to attach to the skin of a user, the interface side of the dermal patch (550, 2008) comprising a first part of the two-part releasable attachment arrangement, and the user interface patch (552, 2007) comprising an interface side and patient side, the patient side of the user interface patch (552, 2007) comprising a second part of the two-part releasable attachment arrangement, the second part being complementary to the first part, the interface side of the user interface patch (552, 2007) being attachable to the nasal cannula, and wherein the nasal cannula comprises: at least one nasal prong, each said prong having a gas outlet adapted to be inserted into a user's nare and a gas inlet fluidly connected to the gas outlet, the at least one nasal prong comprising a backing, the backing configured to rest on a user's face, wherein a lip extends about at least a part of the perimeter of a rear surface of the backing, the rear surface configured for receiving or retaining the user interface patch. at least one nasal prong, each said prong having a gas outlet adapted to be inserted into a user's nare and a gas inlet fluidly connected to the gas outlet, the at least one nasal prong comprising a backing, the backing configured to rest on a user's face, wherein a lip extends about at least a part of the perimeter of a rear surface of the backing, the rear surface configured for receiving or retaining the user interface patch.