Chondrus crispus and other red seaweeds

Sea moss

No human trial supports the popular claims for sea moss (Irish moss, Chondrus crispus), whether for thyroid health, immunity or its '92 minerals'; it is a seaweed with small amounts of some minerals, and LactMed notes that no medicinal value has been proven. The caution that matters most is iodine: measured levels in dried Irish moss differ almost fifty-fold between studies, and case reports link sea moss to dangerous thyroid over-activity.

It can also carry arsenic, cadmium, lead and mercury, so anyone with thyroid disease, or who is pregnant or breastfeeding, should ask a clinician before eating it regularly.

Written by

Healthy and Herbal editorial team

Reviewed by

Healthy and Herbal editors

Updated

10 October 2026

Dried pale sea moss in a bowl next to a jar of sea moss gel

At a glance

Last reviewed 10 October 2026

Evidence

Traditional

Best for

Minerals (small amounts)

Typical form & use

Dried seaweed or gel; no studied dose

Onset

4+ weeks

Safety

Iodine varies widely and can upset the thyroid. 1 known interaction, most serious with thyroid medication.

Check with your medications →

What it's used for

Evidence is rated per use. The same ingredient can be strong for one thing and traditional for another.

Use	Evidence	What the research shows
Minerals and vitamins ('92 minerals')	Traditional	The USDA record for raw Irish moss lists 10 minerals, not 92, and no iodine value; one tablespoon (10 g) gives about 5 kcal, 0.9 mg iron, 14 mg magnesium, 7 mg calcium and 18 µg folate. We found no published analysis supporting the '92 minerals' claim and no trial testing sea moss as a way to correct any deficiency. The elements it does carry include arsenic, lead, cadmium and mercury from the water it grew in.^9,4
Thyroid support	Traditional	We found no trial showing sea moss helps any thyroid condition, but we did find harm: in one case report a woman's Graves' disease worsened while she used an Irish sea moss and bladderwrack supplement and improved after she stopped, and in another a woman developed thyroid storm after six days of fruit juice and sea moss supplements. People with existing or previously treated thyroid disease are most susceptible to iodine excess.^5,6,10
Iodine supply	Traditional	Sea moss does supply iodine, but not predictably. A Spanish analysis found about 3.9 mg per kg of dried Irish moss, while EFSA's dataset for dried carrageen mosses (4 samples) averaged about 186 mg per kg. At those figures, 4 g of dried moss would hold roughly 15 µg or 740 µg of iodine, the second above the 600 µg adult upper limit (our calculation).^2,1
Immunity, gut health and energy	Traditional	These are among the commonest marketing claims, but we found no human trial of sea moss for any of them. LactMed's record describes sea moss as used as food and medicine although no medicinal value has been proven.⁴

How much

Ranges below are what studies used and what supplements commonly contain. They are not a recommendation for you. Start at the low end.

Studied dose

None⁴

No human trial has tested sea moss for a health outcome, so there is no evidence-based amount. The DIY gel and shop-bought gels are foods, not measured doses.

Iodine in dried Irish moss

About 3.9 to 186 mg per kg^2,1

The lower figure is the mean of a Spanish product analysis of Irish moss; the higher is EFSA's mean for 4 dried carrageen moss samples (fresh samples averaged about 32 mg per kg). Products are rarely labelled with their iodine content.

Iodine upper limit

600 µg a day (adults); 200 µg (ages 1–3)^1,8

Set by the EU Scientific Committee on Food in 2002 for total iodine from all sources, and applied to pregnant and breastfeeding women too.

Carrageenan (food additive) ADI

75 mg per kg body weight a day⁷

The group acceptable daily intake for purified carrageenan (E 407) and processed Eucheuma seaweed (E 407a), which EFSA kept in 2018 but called temporary until better data arrive. It applies to the additive, not to eating whole sea moss.

Timing · No source we read gave timing advice, because there is no studied dose.With food? · Sea moss is eaten as a food, usually as a gel stirred into smoothies or puddings; no source we read gave food guidance for a health effect.How long to trial · There is no proven benefit to trial. Thyroid harm in the case reports appeared after anything from six days of heavy use to intermittent use over two years, so watch for palpitations, tremor, weight loss or anxiety and see a doctor if they appear.

How people take it

Dried whole sea mossNo studied amountIn 53 dried products bought online in the US, arsenic, cobalt and mercury were detected, and bacteria and moulds were common. Choose a seller who names the species and where it was harvested.

Sea moss gelNo studied amountSoaked and blended dried moss; see our guide to making it. In 13 shop-bought gels, arsenic and cobalt were below detection and mercury was at trace levels, but pH and microbial quality varied widely, so treat it as a perishable food.

Capsules, gummies and blendsVaries by productOften combined with bladderwrack, a brown seaweed; one case report of worsened Graves' disease involved such a blend. Labels rarely state iodine content.

Carrageenan (E 407)Food additive onlyThe gelling agent first extracted from Irish moss, now made mostly from Eucheuma seaweeds. It is a purified food additive, not a sea moss supplement.

Safety

Who should avoid

Thyroid disease, now or in the past — seaweed iodine can trigger over-activity
Taking thyroid medication — ask your prescriber before eating sea moss regularly
Pregnancy — high seaweed iodine may risk maternal health; ask your midwife
Breastfeeding — LactMed advises avoiding it unless iodine and metals are shown low
Children — the iodine upper limit for ages 1–3 is a third of the adult limit
Weakened immunity — sea moss products have carried bacteria including Salmonella

Known interactions

CautionThyroid medication — Iodine from sea moss can push a vulnerable thyroid into over-activity, as in a case report where it worsened Graves' disease, so it could work against treatment; we found no study of sea moss with thyroid drugs directly.

Questions people ask

Does sea moss really contain 92 minerals?

We found no published analysis that supports the claim. The USDA's nutrient record for raw Irish moss lists 10 minerals, in modest amounts, and sea moss can also carry unwanted elements such as arsenic, lead, cadmium and mercury.

Is sea moss bad for your thyroid?

It can be. Its iodine content is unpredictable, and case reports describe sea moss worsening Graves' disease and, in another woman, thyroid storm after six days of sea moss supplements. People with a thyroid condition, or a past one, are the most susceptible.

Does sea moss contain heavy metals?

It can. A 2026 study of 53 dried sea moss products sold online detected arsenic, cobalt and mercury, and EFSA's data for dried carrageen mosses averaged about 23 mg of total arsenic, 0.8 mg of cadmium and 0.4 mg of lead per kg.

EFSA concluded that seaweed is a relevant source of heavy metals and iodine for the people who eat it, with iodine the main concern.

Is the carrageenan in sea moss safe?

Food-grade carrageenan is a permitted additive. EFSA's 2018 review found it is not absorbed intact and raised no cancer or genetic-damage concern, but called its acceptable daily intake temporary because of data gaps, including whether it affects inflammatory bowel disease, and said it remains inadvisable in infant formula fed from birth.

Those findings are about the purified additive; we found no safety assessment of eating whole sea moss gel.

Make it yourself

DIY guides that use sea moss, with quantities, safety notes and an honest word on what they do.

A glass jar of pale homemade sea moss gel with a little dried sea moss beside it on a bright kitchen counter

How to Make Sea Moss Gel at HomeEasy · 20 min hands-on

Sources (10)

Reader notes

Experiences and questions from readers, read by an editor before they appear. They are personal accounts, not evidence, and are not medical advice.

Last reviewed 10 October 2026 · Next review April 2027 · How we rate evidence

Sea moss

At a glance

What it's used for

How much

How people take it

Safety

Who should avoid

Known interactions

Questions people ask

Does sea moss really contain 92 minerals?

Is sea moss bad for your thyroid?

Does sea moss contain heavy metals?

Is the carrageenan in sea moss safe?

Make it yourself

Sources (10)

Reader notes

Used it? Share how it went, or ask a question.