Sea Moss (Eucheuma & Gracilaria): Nutrients, What Research Shows and Safety

"Sea moss" is a market name, not one plant. On labels it can mean red seaweeds such as Irish moss (Chondrus crispus), or the tropical red seaweeds Eucheuma and Kappaphycus, or sometimes Gracilaria. The USDA entry this page uses is a cultivated Eucheuma type (Canadian cultivated EMI-TSUNOMATA), sold dry and eaten rehydrated. [1] [2] People eat it, or blend it into a gel, for minerals and fiber. This page looks at it as a food. It keeps claims apart from the facts, and it does not repeat the longer claim checks on our other pages: see sea moss gel: claims checked and Irish moss.

Read this first

• Iodine is the first safety point. Seaweed iodine varies hugely. A Norwegian survey of 96 seaweed products found 128 to 62,400 micrograms (mcg) of iodine per portion in whole-food seaweed products, and 54 products would exceed the iodine upper level in one portion. [5] We did not find a measured iodine value for sea moss (Eucheuma, Kappaphycus) itself, and USDA lists none. [1] [2]
• Upper levels: the American Thyroid Association gives 1,100 mcg a day as the US upper limit for adults, and says more than that may cause thyroid problems. [3] The EU upper level for adults is 600 mcg a day. [6]
• Thyroid disease, thyroid medicine, pregnancy, breastfeeding: ask a clinician first. High-dose iodine with anti-thyroid medicines can add to their effect and cause an underactive thyroid. [4] The ATA advises against iodine and kelp supplements above 500 mcg a day, including in pregnancy and breastfeeding. [3]
• Products vary. A 2026 test of 66 sea moss products bought online found bacteria in both dried products and gels, and arsenic, cobalt and mercury in dried products. [8]
• Evidence in one line: we found no human trial of sea moss for any health claim. A 2019 review says more human studies are needed for seaweed in general. [7]
• If you have trouble breathing or swelling of the face or throat after eating anything, call 911 (or your local emergency number).

What is in it (USDA values)

USDA FoodData Central (SR Legacy) has two entries for "Canadian cultivated EMI-TSUNOMATA", a Eucheuma carrageenan seaweed: dry (FDC 167602) and rehydrated (FDC 167603). [1] [2] They are different forms, so they are shown in separate columns. USDA household portions are 0.25 cup dry (5 g) and 0.25 cup rehydrated (25 g). Serving values below are the 100 g values scaled to that portion.

For the dry form, one 5 g portion gives about 3.3 mg iron (18% DV), 0.29 mg manganese (13% DV) and 217 mg sodium (9% DV). [1] % Daily Value uses the FDA 2016 Daily Values. Values vary with species, harvest place, season and processing: a Madagascar study of Eucheuma denticulatum found minerals up to 39.5% of dry weight, with the amount changing across the seasons. [10] Dried Kappaphycus lots from four Indonesian sites differed in ash (30.8 to 39.9%), salt (9.2 to 19.9%) and carrageenan yield (15.1 to 27.0%). [9]

USDA lists no iodine and no vitamin K for these entries. [1] [2] USDA also lists a vitamin B-12 value (2.25 mcg per 100 g dry), but a food table does not show whether that is active B12 or look-alike molecules called analogues, so do not use it as a B12 source. See seaweed and vitamin B12 claims checked.

Plant compounds: the main structural compound is carrageenan, a sulfated seaweed sugar. Regulators define the food additive carrageenan as the refined extract of red seaweeds in the families Gigartinaceae and Solieriaceae, including Eucheuma cottonii. [11] Whole sea moss and the purified additive are not the same thing. See carrageenan.

What research says

Observational findings and lab results do not prove benefit in people. We did not read funding details for the studies above.

How much is a normal serving

The USDA household portions are 0.25 cup dry (5 g) or 0.25 cup rehydrated (25 g), with about 13 kcal or 8 kcal. [1] [2] That is information from the USDA data, not a prescription. We found no official serving size for sea moss and no standard gel amount in the sources we read, so we give none. Because iodine in sea moss is unmeasured in the sources we read, no "safe amount" can be stated. [5] [6]

Safety, allergy and medicines

• Iodine and thyroid: very high iodine can reduce thyroid function. [4] In the UK survey of 224 seaweed products, estimated iodine per serving had a median of 585 mcg, and 26 products could pass the EU adult upper level (the authors note this relied on assumptions). [6] Anyone with thyroid disease should ask their own clinician. See seaweed, iodine and thyroid.
• Thyroid medicines: MedlinePlus says high iodine with anti-thyroid medicines can have an additive effect and could cause hypothyroidism. [4]
• Pregnancy and breastfeeding: the ATA gives a suggested upper limit of 500 to 1,100 mcg a day in pregnancy and breastfeeding and advises against kelp or iodine supplements above 500 mcg. [3] We found no sea moss specific figure. See seaweed in pregnancy and breastfeeding.
• Metals: dried sea moss products had arsenic, cobalt and mercury in the 2026 test; gels had only trace mercury. [8] In dried Kappaphycus from four Indonesian sites, mercury was 0.040 to 1.760, cadmium 0.280 to 0.740 and lead 0.140 to 0.930 mg per kg dried weight. [9] We did not read a safety limit to compare these with, so we draw no verdict. See heavy metals in foods.
• Microbes: Bacillus and Staphylococcus were the most common organisms found in products; Salmonella, Listeria, Vibrio and Escherichia were found less often. [8] People with weak immune systems should ask a clinician. We did not find a source with advice for them.
• Sodium and potassium: the dry form is high in both per 100 g (sodium 4,331 mg, potassium 2,944 mg). [1] A usual portion is small, but people on a low-sodium or low-potassium plan (for example in kidney disease) should ask their care team. See foods, kidney disease, potassium and oxalates.
• Allergy: seaweed allergy: Proper evidence not found in the sources we read. For emergency signs see food allergy basics. Call 911 for trouble breathing or swelling of the face or throat.
• Blood thinners and vitamin K: USDA lists no vitamin K value for these entries, so we cannot say. [1] [2]

Choosing, storing and food safety

• Look for the Latin name on the pack (Eucheuma, Kappaphycus, Chondrus), because "sea moss" alone does not tell you the species. See Irish moss.
• Labels are unreliable on iodine: the Norwegian study found species and iodine content missing or inaccurate on several products. [5] A maker that tests for iodine, metals and microbes is the better choice.
• The 2026 authors call for evidence-based guidance on processing, storage and handling, and the abstract we read gives none. We give no gel recipe or storage times. [8]

Related pages

• Carrageenan
• Irish moss (herb guide)
• Sea moss gel: claims checked
• Iodine in seaweed: how much by type
• Seaweed and vitamin B12 claims checked
• Heavy metals and contaminants in foods