Salt is added to the irrigation water to make its passage more comfortable. Our bodies are made of salt water at a concentration generally agreed to be approximately 0.9 percent, or 9 grams of NaCl (common table salt) per liter. Matching that physiological, or normal, concentration makes the solution more comfortable than either plain water or water with a greater amount of salt. A “physiological” solution is made by placing ½ teaspoon of table salt into 250 ml (or approximately 1 measuring cup) of water. In scientific jargon, this concentration of salt water is also called “isotonic saline.”
Adding salt may do more than just provide comfort. A research protocol using fresh water without any NaCl for their placebo had to be stopped when several of the control subjects developed middle ear infections.
Isotonic saline works to clear mucus and relieve sinus congestion and runny noses. It’s been shown to remove inflammation inducing chemicals like histamine and leukotrienes that the body secretes with allergy. Mucociliary clearance rate, the measure of the speed of removal of mucus, was noted to be increased in allergy patients using 4 ml of isotonic saline twice daily to flush their nasal cavities.
Hypertonic saline, defined as solutions with more than 9 grams per liter of salt, also works. In some studies, a higher salt concentration works better than an isotonic one. Shoseyov and his colleagues used 3.5 percent NaCl, similar to sea water, and achieved better symptom relief in children than when they used a physiological concentration.
While isotonic solutions are thought to work primarily by their mechanical cleaning effect, hypertonic solutions may additionally decrease swelling. Extracellular fluid in the nasal mucosa would theoretically be drawn out towards the area of higher salt concentration by osmosis. There’s conflicting data showing that hypertonic saline may also increase the frequency at which cilia beat, thereby clearing mucus out of the nasal and sinus passageways more rapidly.
Hypertonic solutions might have a downside. Greiff and his colleagues looked at pieces of nasal mucosa in petri dishes and found that increasing concentrations of saline caused the tissue to secrete more mucus and to react more severely to histamine and another stimulating chemical. As this study was done in dissected tissue and not live people, the results should be interpreted with caution.
Investigators in another published report did look at the effects of hypertonic solutions in people. They found that increasing concentrations of saline induced dose-dependent increases in the sensations of pain, blockage, and drippy nose.
In hospitals, hypertonic saline is often used to induce sputum production from the lungs in order to test it for specific bacteria when patients have pneumonia. It has precipitated asthma attacks in some asthmatics and in those with hyper-reactive airways. Adults and children with asthma need to be careful to avoid aspirating hypertonic saline nasal irrigation fluid into their lungs.
The bottom line is that physiological saline has been found to work, and it’s the least likely salt concentration to cause problems. If you’re comfortable using a slightly higher concentration of salt, it may give a better response. The higher the concentration goes beyond what is natural to the body, the more likely there are to be side effects. Don’t go any higher than 3.5 percent, the concentration of sea water. Dr. Rabago, a family physician who studies neti, prefers 2 percent. That would be roughly equivalent to 1 teaspoon per 250 ml or 1 measuring cup of water. He advises patients to adjust the concentrations of salt to their own personal preferences.