Sea salt is at least 90% sodium chloride, the same compound that makes up table salt. The remaining portion, roughly 10% or less, is a mix of trace minerals, moisture, and tiny amounts of naturally occurring elements picked up from the ocean. That small fraction is what gives sea salt its color, texture, and subtle flavor differences, but it doesn’t make sea salt significantly more nutritious than regular table salt.
The Main Ingredient: Sodium Chloride
Sodium chloride dominates the composition of every type of sea salt. Whether you’re buying coarse grey salt from Brittany or fine white flakes from the Mediterranean, at least 90% of what’s in the container is the same molecule found in standard table salt. By weight, both sea salt and table salt are 40% sodium. The practical difference is crystal size: sea salt crystals tend to be larger and more irregular, so fewer fit on a teaspoon, which can mean slightly less sodium per spoonful. But gram for gram, the sodium content is identical.
Trace Minerals in Sea Salt
The remaining fraction of sea salt contains minerals dissolved in ocean water that get left behind during evaporation. The most abundant of these are magnesium, calcium, and potassium, along with sulfates. Seawater contains roughly 1,272 parts per million (ppm) of magnesium, 400 ppm of calcium, and 380 ppm of potassium. Some of those minerals carry over into the harvested salt, though the exact amounts vary depending on where and how the salt is produced.
These trace minerals are responsible for the subtle flavor differences people notice between sea salt and table salt. Magnesium compounds, for example, contribute a slightly bitter edge, while calcium can add a faint mineral sweetness. In practical nutritional terms, though, the quantities are tiny. You’d need to eat an unreasonable amount of sea salt to get meaningful doses of any of these minerals from salt alone.
What Sea Salt Lacks: Iodine
One important thing sea salt does not contain in useful amounts is iodine. Unfortified sea salt has only trace levels of iodine, far below what your body needs. By contrast, iodized table salt in the U.S. contains 45 micrograms of iodine per gram. The recommended daily intake for adults is 150 micrograms, which you can get from roughly half to three-quarters of a teaspoon of iodized table salt. If sea salt is your only salt, you’ll need to get iodine from other sources like seafood, dairy, or eggs.
How Varieties Differ
Not all sea salts have the same mineral profile. The differences come down to geography, water composition, and harvesting technique.
- Celtic sea salt (also called Sel de Guérande) is harvested from clay-lined salt ponds along the coast of Brittany, France. The clay contributes to its grey color and higher magnesium content, up to 10% of the salt’s total weight coming from minerals other than sodium chloride. That extra magnesium gives it a slightly less sharp, less “salty” taste compared to other salts.
- Fleur de sel is the thin crust of delicate crystals that forms on the surface of evaporation ponds. Because it’s skimmed from the top rather than scraped from the bottom, the crystals are lighter, flakier, and retain more moisture. It’s considered the most refined variety of sea salt, prized for texture rather than mineral content.
- Standard sea salt sold in grocery stores is typically washed and sometimes lightly processed, which strips away some of the trace minerals and leaves it closer in composition to regular table salt.
What Sea Salt Doesn’t Have (That Table Salt Does)
Table salt is processed with additives that sea salt typically skips. The most notable are anti-caking agents, chemicals added to keep the fine grains from clumping together in humid conditions. Common ones include calcium silicate, silicon dioxide, and potassium ferrocyanide. These are considered safe at the levels used, but their presence is one reason people reach for sea salt as a “cleaner” option. Sea salt’s coarser, irregular crystals don’t clump as easily, so manufacturers generally don’t add anti-caking agents.
How Production Shapes What’s Inside
The way sea salt is made determines how many trace minerals survive into the final product. Traditional solar evaporation, the oldest method, works by pumping seawater into shallow ponds and letting the sun do the work. As water evaporates, sodium chloride crystallizes first. The leftover liquid, called bitterns, contains higher concentrations of magnesium, potassium, and other minerals. Producers typically drain these bitterns before the final harvest to keep the salt from becoming too bitter, but some mineral residue remains, especially in less processed varieties like Celtic salt.
Industrial vacuum evaporation takes a different approach. The brine is chemically treated with soda ash and caustic soda to remove calcium and magnesium before the salt crystallizes. The result is a very pure sodium chloride product with almost no trace minerals. Salt produced this way is what typically becomes standard table salt, not what you’d find labeled as sea salt.
Microplastics and Heavy Metals
Because sea salt comes directly from ocean water, it also picks up contaminants present in that water. A large study published in Environmental Science & Technology analyzed sea salt brands from around the world and found microplastic particles in the vast majority of them. The range was wide: from zero to over 1,600 particles per kilogram, with a median of 82 particles per kilogram. Salts from regions with higher ocean pollution tended to contain more microplastics.
Heavy metals are also present in small amounts. Testing of commercial salt products has found detectable levels of lead in 96% of salts and arsenic in 100% of them. Mercury, however, was not found in any products tested. The concentrations are generally well below FDA safety thresholds (10 ppm for lead, 3 ppm for arsenic, 1 ppm for mercury), and given how little salt you consume daily, the exposure from salt alone is minimal. Still, these trace contaminants are a natural consequence of harvesting a product directly from the ocean.
Sea Salt vs. Table Salt: The Bottom Line on Composition
The core chemistry is the same. Sea salt is sodium chloride with a small percentage of ocean-derived minerals. Table salt is sodium chloride with added iodine and anti-caking agents. Sea salt offers a broader mineral profile, but in amounts too small to matter nutritionally at normal consumption levels. The real differences are practical ones: texture, crystal size, flavor nuance, and the absence of additives. Those are legitimate reasons to prefer one over the other, but they’re culinary reasons, not health reasons.