Salt is essential not only to life, but to good health. Human blood contains 0.9% salt (sodium chloride) the same concentration as found in United States Pharmacopeia (USP) sodium chloride irrigant commonly used to cleanse wounds. Salt maintains the electrolyte balance inside and outside of cells. Most of our salt comes from foods, some from water. Doctors often recommend replacing water and salt lost in exercise and when working outside. Wilderness hikers know the importance of salt tablets to combat hyperthermia. Oral rehydration involves replacing both water and salt. Expectant mothers are advised to get enough salt. Increased salt intakes have been used successfully to combat Chronic Fatigue Syndrome. Dramatic deficiencies (e.g. "salt starvation" in India) or "excessive" sodium intakes have been associated with other conditions and diseases, such as hypertension and stomach cancer. Testing the salinity of perspiration is a good test for cystic fibrosis; scientists suspect that cystic fibrosis is caused by a deformed protein that prevents chloride outside cells from attracting needed moisture.

Sodium occurs naturally in many foods and is also added in the form of salt or other sodium-containing substances. Common salt or table salt is a chemical compound of sodium and chlorine and is called sodium chloride. The sodium content of food has important implications for health. Salt contains about 40 per cent sodium, and a teaspoon of salt, which weighs about 5 grams, contains about 2 grams of sodium.

Rock salt and sea salt are almost entirely sodium chloride, with only traces of other elements (minerals). In contrast to pepper, which loses flavour once ground, there is no advantage in freshly grinding salt prior to its use. Iodized salt contains about 0.03 milligram of iodine per gram of salt. It is intended as a supplement for people whose diet is deficient in iodine. Recent findings in the U.S.A. indicate that the level of iodine in the diet has increased and that the widespread use of this salt is unnecessary.