While nasal irrigation can be carried out using ordinary tap water, this is not safe and additionally can be uncomfortable because it irritates the mucous membranes. Therefore, an isotonic or hypertonic salt water solution is normally used, i.e. water with enough salt to match the tonicity of the body cells and blood. For the same reason, lukewarm water is preferred over cold water, which in addition to irritating nasal membranes can also exaggerate the gag reflex during irrigation.