Sea moss
Research on what people take sea moss for was not sourced for this page. Irish moss samples averaged 3.86 mg/kg of iodine. A case of iodine-linked thyroid overactivity followed sea moss and bladderwrack use. A test of 66 US online products found arsenic, cobalt and mercury in dried sea moss, and Salmonella and Cronobacter among isolated bacteria.
- Status
- Sold as a food and dietary supplement in the US. Not approved by the FDA as a drug for any use.
- Also called
- Irish moss, Chondrus crispus, sea moss gel, red seaweed, carrageen moss, carrageenan moss
- Taken for
- thyroid health, immunity, gut health, digestion, skin, energy, minerals, libido
Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on
Shown to help0
No benefit shown in research yet.
Reported risks4
- LimitedLimited evidence: Irish moss iodine averaged 3.86 mg/kg in one study, while other reports describe high and widely varying iodine across seaweeds.
- LimitedCase reports: a woman with untreated Graves' disease had thyroid overactivity attributed to iodine from a sea moss and bladderwrack supplement, easing after she stopped.
- LimitedOne study found arsenic, cobalt and mercury in dried US sea moss products, with only trace mercury in gels. Amounts were not compared with limits.
- LimitedOne study found bacteria in dried and gel sea moss products, including Salmonella, Cronobacter and Escherichia species. Illness was not tested.
What people take it for, and what was found
We haven't sourced research on this yet.
Risks
Reported risks4
Iodine content
Limited evidence: Irish moss iodine averaged 3.86 mg/kg in one study, while other reports describe high and widely varying iodine across seaweeds.
The numbers and sources
- Effect
- In 30 samples of red seaweeds from shops, Irish moss had the higher average iodine content, 3.86 ± 1.49 mg/kg dry weight. Four grams a day of dried Irish moss supplied 25.7% of the dietary reference intake for iodine in children. The authors calculated that 286 g a day would exceed the adult upper limit of 1,100 µg [1].
- Population
- 30 samples of dulse and Irish moss [1].
- Sources
- [1]
- Caveats
- Iodine in seaweed varies widely by species. In 14 seaweeds bought in Italy, iodine ranged from 3.4 to 7,316 mg/kg, highest in a kelp [2]. A case report describes Irish sea moss supplements as having high and variable iodine [3], which differs from the low average in [1].
Thyroid overactivity in Graves' disease
Case reports: a woman with untreated Graves' disease had thyroid overactivity attributed to iodine from a sea moss and bladderwrack supplement, easing after she stopped.
The numbers and sources
- Effect
- A 28-year-old woman with fatigue, palpitations and weight loss had TSH below 0.01 mIU/L and raised free T4 (2.46 ng/dL). She had used a store-bought Irish sea moss and bladderwrack supplement on and off for 2 years and was diagnosed with Graves' disease. The authors attributed her thyrotoxicosis to excess iodine (the Jod-Basedow phenomenon). One week after stopping sea moss, free T4 was 1.4 ng/dL [3].
- Population
- One case report [3].
- Sources
- [3]
- Caveats
- A conference abstract. The product also contained bladderwrack, a brown seaweed, and the patient had untreated thyroid disease [3].
Arsenic, cobalt and mercury in US products
One study found arsenic, cobalt and mercury in dried US sea moss products, with only trace mercury in gels. Amounts were not compared with limits.
The numbers and sources
- Effect
- In 66 sea moss products bought from major US online retailers (53 dried, 13 gels), arsenic, cobalt and mercury were detected in dried sea moss. In gels, arsenic and cobalt were below detection limits and mercury was found at trace levels [4]. Across 14 seaweeds sold in Italy, which included Chondrus crispus, total arsenic ranged up to 67.6, cadmium up to 7.2 and lead up to 6.7 mg/kg dry weight [2].
- Population
- 66 US products [4]. 14 seaweeds from Italian specialty stores [2].
- Sources
- [4], [2]
- Caveats
- The abstract of [4] does not give concentrations or compare them with limits. The Italian ranges cover all 14 species, not Chondrus crispus alone [2].
Bacteria in products
One study found bacteria in dried and gel sea moss products, including Salmonella, Cronobacter and Escherichia species. Illness was not tested.
The numbers and sources
- Effect
- Mean total plate counts were 4.30 log CFU/g in dried sea moss and 3.92 in gels. Presumptive Bacillus and Staphylococcus were recovered from both forms, and Escherichia, Salmonella, Listeria and Vibrio less often. Isolates identified included Salmonella, Cronobacter and Escherichia species. Gel pH ranged from 2.71 to 7.05 [4].
- Population
- 66 US products [4].
- Sources
- [4]
- Caveats
- Listeria and Vibrio were not confirmed among sequenced isolates [4]. The study did not test for illness.
Sources
- Darias-Rosales J, Rubio C, Gutiérrez ÁJ, et al. Risk assessment of iodine intake from the consumption of red seaweeds (Palmaria palmata and Chondrus crispus). Environmental Science and Pollution Research. 2020. https://doi.org/10.1007/s11356-020-10478-9
- Desideri D, Cantaluppi C, Ceccotto F, et al. Essential and toxic elements in seaweeds for human consumption. Journal of Toxicology and Environmental Health, Part A. 2016. https://doi.org/10.1080/15287394.2015.1113598
- Khalifa M, Aftab HB, Kantorovich V. "Fueling the Fire" - Irish Sea-Moss Resulting in Jod-Basedow Phenomenon in a Patient With Grave's Disease. Journal of the Endocrine Society. 2021. https://doi.org/10.1210/jendso/bvab048.1849
- Rejuso A, Çobo M, Curran JE, et al. Microbial and Heavy Metal Analyses of Commercially Available Sea Moss and Sea Moss Products. Journal of Food Protection. 2026. https://doi.org/10.1016/j.jfp.2026.100915