Various mutations of the cystic fibrosis gene block the "gates" that allow the flow of salt across the cell membranes. This causes mucus to become thick and clog the lungs. Tezacaftor is a "cystic fibrosis transmembrane conductance regulator (CFTC) corrector". The CFTR protein is a channel at the surface of the cells that allows the movement of particles such as chloride in and out of the cell, contributing to salt and water balance. Tezacaftor corrects the positioning of the CFTR protein on the cell surface to permit proper channel formation and improved flow of water and salts across the cell membrane.  The thick mucus is reduced and cystic fibrosis symptoms lessen.