Why is a true allergy to pure salt water generally considered impossible?

The human body naturally contains salt and water, making the body unable to mount an immune response against its own necessary components.

Mounting a true allergic reaction, which involves the immune system identifying a substance as a foreign threat, against pure seawater is widely considered biologically implausible. This impossibility stems from the fundamental physiological fact that the human body inherently requires and naturally maintains significant concentrations of salt (sodium chloride) and water within its cells and bodily fluids. Because salt is an integral, necessary component of normal human biology, the immune system is structured to recognize and tolerate its presence, thereby precluding the typical mechanism required for developing an immune-mediated allergic response against it.