Sea Moss
Chondrus crispus
TL;DR
Sea moss (Irish moss, Chondrus crispus) is an edible red seaweed with no proven health benefits in human trials. It adds some minerals and carrageenan, but products vary in iodine, heavy metals and microbial quality.
Ideal For
- Cooks using it as a plant-based thickener
- Adults without thyroid disease eating small food amounts
Avoid If
- You have thyroid disease, unless your clinician agrees
- You are breastfeeding and the product's iodine and metal levels are untested
- You take methimazole or other antithyroid treatment
- You have ulcerative colitis and want to avoid carrageenan
- You are pregnant, without checking total iodine with your clinician
Frequently Asked Questions
What are the benefits of sea moss?
Does sea moss really contain 92 minerals?
Is sea moss good for your thyroid?
Is sea moss safe to eat every day?
Does sea moss boost the immune system?
Can sea moss help with weight loss?
Overview
Sea moss usually means Irish moss (Chondrus crispus), a red seaweed eaten as food and sold dried, as a soaked and blended gel, and in supplements. The name is also used for other red seaweeds, such as Kappaphycus alvarezii, known as elkhorn sea moss. The NIH's LactMed database states its status plainly: sea moss is used as food and medicine, although no medicinal value has been proven.
Most of what sea moss is credited with comes from laboratory work on its components, not from people eating it. Its main carbohydrate is carrageenan, a gelling fibre that is also a common food additive (E 407). In a lab model of human gut fermentation, whole Chondrus crispus increased bacteria such as Akkermansia muciniphila, but that has not been tested in people. A review of edible seaweeds concluded that more human intervention studies are needed before their health claims can be substantiated.
Nutritionally, raw Irish moss is mostly water (81%). Per 100 g, USDA FoodData Central lists 49 kcal, 1.5 g protein, 1.3 g fibre, 8.9 mg iron, 144 mg magnesium, 72 mg calcium and 182 mcg folate, and no vitamin B12. Its iodine is modest next to kelp: 30 samples of red seaweed analysed in Spain put Irish moss at 3.86 mg per kg dry weight, and the authors judged 4 g of dried Irish moss a day to pose no iodine risk.
The practical concerns are product quality and who is taking it. A 2026 analysis of 66 sea moss products bought online in the US detected arsenic, cobalt and mercury in dried sea moss, found presumptive Salmonella and other bacteria in some products, and measured gel acidity anywhere from pH 2.71 to 7.05. Extra iodine matters most for people with existing thyroid disease, and LactMed advises avoiding sea moss while breastfeeding unless its iodine and heavy metal levels have been shown to be safe.
How It Works
- Carrageenan, the main gelling polysaccharide in sea moss, is not absorbed intact; EFSA's 2018 review kept a temporary acceptable daily intake of 75 mg/kg body weight for the additive.
- In a lab model of human gut fermentation, whole Chondrus crispus acted like a prebiotic, raising bacteria such as Akkermansia muciniphila; no human trial has confirmed this.
- It supplies iodine, which the thyroid needs to make the hormones T4 and T3, but in modest and variable amounts compared with brown seaweeds such as kelp.
- Like other seaweeds it takes up metals from the water it grows in; arsenic, cobalt and mercury have been detected in dried commercial sea moss.
Quick Facts
- Usually Irish moss, a red seaweed
- No human trials of its health claims
- Main fibre is carrageenan (E 407)
- Much less iodine than kelp
- Metals detected in dried products
- LactMed: avoid when breastfeeding unless tested
Benefits & Outcomes
No linked outcomes yet. Research is ongoing.
Health Concerns Addressed
No linked health concerns yet.
Supporting Research5 studies
Microbial and Heavy Metal Analyses of Commercially Available Sea Moss and Sea Moss Products
Rejuso A, Çobo M, Curran JE +4 more
evaluated 66 sea moss products purchased from major online retailers
Risk assessment of iodine intake from the consumption of red seaweeds (Palmaria palmata and Chondrus crispus)
Darias-Rosales J, Rubio C, Gutiérrez ÁJ +2 more
the consumption of 286 g/day of Irish moss would lead to exceeding the UL
Risks and benefits of consuming edible seaweeds
Cherry P, O'Hara C, Magee PJ +2 more
more evidence from human intervention studies is needed
A randomized trial of the effects of the no-carrageenan diet on ulcerative colitis disease activity
Bhattacharyya S, Shumard T, Xie H +4 more
Carrageenan intake contributed to earlier relapse in patients with ulcerative colitis
Randomized controlled pilot study: effect of carrageenan emulsifier on inflammation and gastrointestinal symptoms in quiescent ulcerative colitis
Laatikainen R, Lehto M, Mäkelä-Salmi N +3 more
short-term usage of food-grade carrageenan is safe among people with UC
Safety Information
Potential Side Effects
Human trials of sea moss itself have not been run, so side effects have not been recorded systematically. The known risks are excess iodine in susceptible people, heavy metals, and bacterial contamination found in some commercial products. In two very small trials of carrageenan capsules in ulcerative colitis, one linked carrageenan to earlier relapse and the other found no short-term harm.
Contraindications
Existing thyroid disease, because people with pre-existing thyroid disorders are more susceptible to thyroid dysfunction from extra iodine. Breastfeeding, unless the product's iodine and heavy metal levels have been shown to be safe (LactMed).
Drug Interactions
- Antithyroid drugs such as methimazole: high iodine intake can add to their effect and cause hypothyroidism; ask your prescriber before using iodine-containing seaweed.
Pregnancy & Breastfeeding
Pregnancy: Not enough evidence to judge
Breastfeeding: Likely unsafe
Dosage Guidelines
Dosage Used in Studies
Consult healthcare provider
Best Time to Take
No timing has been studied in people, because no trial has tested sea moss for a health outcome. It is eaten as a food, so there is no evidence-based schedule to follow.
Best Form
No form has trial evidence. If you use it, choose dried Irish moss or gel from a seller that tests for heavy metals and microbes.
Bioavailability
Carrageenan is not absorbed intact (EFSA 2018). We found no human data on how well the minerals in sea moss are absorbed.
Dosing by Goal
| Goal | Dose | Notes |
|---|---|---|
| Clinical dose | None established | No human trial has tested sea moss for any health outcome, so there is no evidence-based dose. |
| Dried Irish moss as food (adults) | About 4 g dried per day or less | One iodine risk assessment found 4 g/day posed no iodine risk; the adult upper limit of 1,100 mcg iodine/day would only be passed at about 286 g/day of the samples tested. Other seaweed species, and blends with kelp, can carry far more iodine. |
Forms Compared
Dried sea moss
Best for Home-made gel, cooking
Soaked and rinsed before use. A 2026 US survey detected arsenic, cobalt and mercury in dried products.
Sea moss gel
Best for Smoothies, recipes
Ready-made gels varied widely between products in acidity (pH 2.71-7.05) and sugar content (0.8-46.1 degrees Brix).
Medical Disclaimer
The information provided on this website is for educational and informational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or before starting any supplement regimen.
Individual results may vary. The statements on this website have not been evaluated by the Food and Drug Administration. Products and information are not intended to diagnose, treat, cure, or prevent any disease.