Cell-cell fusion occurs when the plasma membranes of neighboring cells fuse to form a multinucleated cell. To fuse, lipid bilayers of cell membranes must come into very close contact, in the range of several angstroms. To achieve this degree of close proximity, the two surfaces must become at least partially dehydrated as water bound to the membrane enhances polar repulsion of membranes. Next, one or both bilayers must be destabilized in some way, inducing a localized rearrangement of the bilayers. If both bilayers are destabilized, an aqueous bridge is formed and the cytoplasmic contents of both cells mix.