Barotrauma may be caused when diving, either from being crushed, or squeezed, on descent or by stretching and bursting on ascent; both can be avoided by "equalising" the pressures. A negative, unbalanced pressure is known as a squeeze, crushing eardrums, dry suit, lungs or mask inwards and can be equalised by putting air into the squeezed space. A positive unbalanced pressure expands internal spaces rupturing tissue and can be equalised by letting air out, for example by exhaling. Both may cause barotrauma. There are a variety of techniques depending on the affected area and whether the pressure inequality is a squeeze or an expansion: