Research · Seaweed and skin

Types of seaweed: what each offers skin, and what studies show.

Brown, red and green seaweeds are chemically very different, and so is the research on them. This guide reads the studies on fucoidan, phlorotannins and ulvan, separates what was shown in a test tube from what was shown in people, and covers iodine, contaminants and allergy. Every claim cites its source.

Translucent golden-olive kelp fronds drifting in calm seawater in soft light

3 groups
Brown, red and green algae are the groups reviewed for skin effects, each with different bioactive compounds.²
24.2% to 26.8%
Tyrosinase inhibition by polysaccharides from three red seaweeds in a laboratory assay. It is an enzyme test, not a skin trial.⁷
120 people
Healthy volunteers in the one human study we found: a cream with 1% ulvan enhanced hydration. Some authors work for companies that make seaweed and cosmetics.⁹
50% and 35%
Share of Indonesian seaweed-based food products with lead and with arsenic detected. Most were assessed as safe for consumption.¹²

The short answer

Three colours, three chemistries. Brown seaweeds are studied for fucoidan and phlorotannins,³⁸ red for galactose-based polysaccharides,⁷ and green for ulvan.⁹
Most results are from the lab. Of the 14 sources here, six are enzyme or cell studies and three are reviews of that work. They show activity in a tube or a dish, not a change in skin.³⁴⁷
One human study. A cream with 1% ulvan and thermal spring water enhanced hydration in 120 volunteers, and some authors work for companies that make seaweed and cosmetics.⁹
Eating it carries its own risks. Iodine, trace metals and allergy are documented for seaweed as food, and we found no study of these for skincare.¹⁰¹²¹³

01 · Three families

Sorted by colour, defined by chemistry.

A 2024 review of seaweed in atopic dermatitis explores the brown, red and green algae and names their shared bioactive groups: polysaccharides, phlorotannins, polyphenols and chlorophyll.² A 2019 review adds that seaweed compounds are studied for three skin problems: hyperpigmentation, premature skin aging and acne.¹

The groups are not interchangeable. Which compound is present, and how it is extracted, changes what an extract does, so a label that says only “seaweed” tells you very little.⁵⁸

Three pieces of dried seaweed, olive-brown, rose-red and pale green, on cream linen

Brown
olive, golden and dark brown
Fucoidan and phlorotannins
Fucoidans are fucose-rich sulfated polysaccharides derived mainly from brown seaweeds.⁸ Phlorotannins are phenolic compounds studied for antioxidant, enzyme-inhibiting and tyrosinase-inhibiting activity.³⁵⁶
Brown seaweed in depth
Red
rose to deep red
3,6-anhydro-galactose polysaccharides
Polysaccharides from six red seaweeds contained 3,6-anhydro-galactose with galactose in molar ratios from 1.0:1.0 to 1.0:3.1, and three showed tyrosinase inhibition in the lab.⁷
Red seaweed in depth
Green
fresh and pale green
Ulvan
Ulvan from green seaweed was made at 80% carbohydrate purity, with 34% rhamnose and 11% sulfate, and tested at 1% in a hydrating cream.⁹
Green seaweed in depth

02 · Brown seaweed

Fucoidan and phlorotannins, in the lab.

Phlorotannin-rich fractions

Fractions of Fucus spiralis were tested for antioxidant, enzyme-inhibiting, anti-inflammatory and photoprotective capacity. The best one inhibited collagenase at 0.037 µg/mL and elastase at 3.0 µg/mL, and cut UVB-induced ROS (IC50 31.3 µg/mL).³
A second brown seaweed’s ethyl acetate fraction inhibited collagenase, elastase and tyrosinase, reduced UVA and UVB ROS in mouse 3T3 cells, and lowered TNF-α and IL-6 in mouse macrophages.⁴
Both groups link the effects to phenolic compounds such as phlorotannins.³⁴

How the extract is made matters

Three purification methods applied to one Djibouti brown alga enriched different phlorotannins. The liquid-liquid fraction held the most complex mix, including phloroglucinol, diphlorethol/difucol, fucophlorethol and bifuhalol.⁵
An ultrasound extract of Dictyopteris justii inhibited tyrosinase with an IC50 of 0.51 mg/mL, against 46.61 µg/mL for kojic acid.⁶
By those figures the extract was roughly eleven times weaker than kojic acid, although the authors call the activity significant.⁶

A glossy green-gold seaweed ribbon curling over a dome of clear gel on pale stone

Fucoidans are structurally diverse, fucose-rich sulfated polysaccharides derived mainly from brown seaweeds. A 2026 review says the evidence supports an antioxidant effect, including in skin and wound healing, but that translation is limited by differences in source species, extraction, purification and molecular weight.⁸ It calls for standardized chemistry and better pharmacokinetic data. Two of the authors work for a fucoidan producer.⁸

How to read this. Activity in an enzyme test or a cell dish is a first step. The brown seaweed studies here did not test a cream on skin, so they cannot say whether a product would change it.

03 · Red seaweed

Polysaccharides and the pigment enzyme.

A 2020 study analysed polysaccharides from six red seaweeds by gas chromatography-mass spectrometry. All contained 3,6-anhydro-galactose, with molar ratios to galactose from 1.0:1.0 to 1.0:3.1. Polysaccharides from three of the species, and their degradation products, inhibited tyrosinase by 24.2% to 26.8%.⁷

The authors suggest the method could serve quality control and that these polysaccharides are potential cosmeceutical ingredients.⁷ That is a statement about potential. The test measured an enzyme, not skin colour.

A 2025 study of seaweed extracts found that lipophilic extracts had the strongest anti-tyrosinase activity, and used computer modelling to point to stigmasterol as a candidate. Its safety findings came from cell tests and predictions.¹⁴

04 · Green seaweed

Ulvan, the one that met people.

What was tested

Ulvans were obtained by hydrothermal treatment and a solvent-free concentration step, giving 80% carbohydrate purity, 34% rhamnose, 11% sulfate and a size above 10 kDa.⁹
Hydrating creams with 1% ulvan and low-mineralization thermal spring water showed a more marked shear-thinning behaviour, which the authors say suggests better spreadability.⁹

What 120 volunteers showed

Objective and subjective evaluation indicated enhanced skin hydration from ulvan and from the thermal spring water, with an additive effect.⁹
All creams reduced the tightness sensation, and scaling was significantly reduced in the ulvan group, with high tolerance.⁹
It was a hand-cream study in healthy volunteers. Some authors work for a seaweed producer and a cosmetics company.⁹

What this supports. Hydration of the hands in healthy adults over the study period. It does not address wrinkles, pigment or the face, and the design did not separate ulvan from the spring water on its own.

For how kelp extract is used in a Vanu Health formula, see our kelp extract ingredient page.

05 · Evidence at a glance

What kind of evidence is this?

The bars sort the 14 sources on this page by the kind of study. Most are laboratory work, and only one involved people using a skincare product.

Laboratory enzyme and cell studies6Tubes and cell cultures, not skin^{3, 4, 5, 6, 7, 14}
Reviews of the above3Summaries of laboratory and animal work^{1, 2, 8}
Human volunteers1One hydrating cream, 120 people⁹
Safety reports and analyses4Case reports, a letter and contamination testing^{10, 11, 12, 13}

Studies on seaweed and skin: what was studied, the type of study, what was measured and the result
What was studied	Study type	What was measured	Result
Brown seaweed Fucus spiralis fractions	Lab: enzyme and cell tests	Antioxidant, collagenase, elastase, UVB-induced ROS	The most active fraction inhibited collagenase (0.037 µg/mL) and elastase (3.0 µg/mL) and reduced UVB-induced ROS (IC50 31.3 µg/mL). The authors link this to phlorotannins.³
A brown seaweed, five fractions	Lab: enzyme and cell tests	Antioxidant, collagenase, elastase, tyrosinase, ROS, TNF-α and IL-6	The ethyl acetate fraction inhibited collagenase, elastase and tyrosinase (IC50 7.2, 4.8 and 85.9 µg/mL), reduced UVA and UVB ROS in mouse cells and lowered TNF-α and IL-6.⁴
A brown macroalga from Djibouti, three purified fractions	Lab: chemistry and enzyme tests	Phenolic content, antioxidant, tyrosinase and elastase inhibition	The purification method changed which phlorotannins were enriched; the most structurally complex fraction was also the most bioactive, which the authors say is likely linked.⁵
Brown macroalga Dictyopteris justii extract	Lab: enzyme test	Tyrosinase inhibition against kojic acid	IC50 of 0.51 mg/mL against 46.61 µg/mL for kojic acid, so it was much weaker than the reference.⁶
Six red seaweeds, polysaccharides	Lab: chemistry and enzyme test	3,6-anhydro-galactose, tyrosinase inhibition	Three polysaccharides inhibited tyrosinase by 24.2% to 26.8%.⁷
120 healthy volunteers, creams with 1% ulvan and thermal spring water	Human: cosmetic study	Skin hydration, tightness, scaling, tolerance	Enhanced hydration with ulvan and spring water, scaling reduced in the ulvan group, high tolerance. Some authors work for a seaweed producer and a cosmetics company.⁹

What the reviews conclude. The 2024 atopic dermatitis review says seaweeds modulate immune responses, reduce epidermal thickness and restore skin barrier function, and that further clinical studies are needed to confirm efficacy and set dosing.² We take the second half of that sentence as the headline.

06 · Safety

Iodine, trace metals and allergy.

Iodine

A 2024 case report describes primary hypothyroidism from excessive daily seaweed consumption for health purposes, and notes that regular intake made the cause hard to spot.¹⁰

Trace metals

In Indonesian seaweed-based food products, lead was found in 50% of samples, arsenic in 35%, cadmium in 25% and mercury in 5%. A quarter of the contaminated samples exceeded national limits, and most products were judged safe to eat.¹²

Processing and allergy

In brown seaweed Alaria esculenta, drying, ultrasound and microwave treatments reduced trace elements and iodine.¹¹ A 2018 letter reports a case of seaweed allergy.¹³

An honest limit. These findings concern seaweed eaten as food. We found no study measuring iodine uptake, contaminant levels or allergy from seaweed in skincare, so we make no safety claim for it either way.

07 · Reading a claim

Five questions to ask of any seaweed claim.

Which seaweed, which compound?
Fucoidan, phlorotannins and ulvan are different molecules from different colours of seaweed.⁸³⁹ “Seaweed extract” alone does not say which.
Test tube or skin?
Enzyme inhibition and cell results³⁷ are not results on people. Look for a trial that used the product on skin.
How strong, against what?
One brown seaweed extract was about eleven times weaker than kojic acid in the same assay.⁶ A reference comparison tells you more than “inhibits tyrosinase”.
Who ran the study?
The ulvan cream study and the fucoidan review each include authors from producers.⁹⁸ It is disclosed, and worth weighing.
Eaten or applied?
The iodine, contaminant and allergy reports are about food.¹⁰¹²¹³ The hydration result is for a cream.⁹ Do not carry results from one to the other.

08 · What we could not confirm

The gaps, stated plainly.

A clinical trial of any seaweed extract on wrinkles, firmness or pigmentation. We found only laboratory work and one hydration study.¹⁹
Whether fucoidan, phlorotannins or ulvan penetrate the skin from a cream. The studies we read did not measure it.
That seaweed “detoxifies” skin, or that its mineral content is absorbed through it. We found no study we could read, so we make no claim.
Yearly or percentage improvements in skin from seaweed. We found none in a human study.
Comparisons between named species, such as kelp, wakame, nori or dulse, on skin outcomes. We did not find studies that make them.
Iodine, trace-metal or allergy risk from seaweed in skincare.¹⁰¹²¹³
Sustainability and harvesting claims. We did not review them.

Vanu Health’s DermaGlass® masks are hydrating skincare. This page makes no seaweed, whitening, firming or anti-aging claim about them or any other Vanu Health product.

09 · Questions

Frequently asked questions.

What are the main types of seaweed in skincare research?

The reviews we read sort seaweeds into brown, red and green algae. Brown seaweeds are the source of fucoidan, a fucose-rich sulfated polysaccharide, and of phlorotannins, a group of phenolic compounds. Red seaweeds were studied for their polysaccharides, which contain 3,6-anhydro-galactose. Green seaweeds are the source of ulvan, which was tested in a hydrating cream. ^{2, 3, 7, 8, 9}

Does seaweed lighten skin or fade dark spots?

The evidence we found is from laboratory enzyme tests, not from people. Extracts and polysaccharides from several seaweeds inhibited tyrosinase, the enzyme in melanin production. Red seaweed polysaccharides inhibited it by 24.2% to 26.8%. A phlorotannin-rich brown seaweed extract had an IC50 of 0.51 mg/mL, compared with 46.61 µg/mL for kojic acid, so it was far less potent in that assay. ^{6, 7, 14}

Can seaweed reduce wrinkles or stimulate collagen?

We found no human trial of a seaweed product on wrinkles. In laboratory tests, brown seaweed fractions inhibited collagenase and elastase, enzymes that break down skin matrix, and lowered reactive oxygen species made by UVB in cells. These are cell and enzyme results. They do not show a change in a person’s skin. ^{3, 4}

Does seaweed hydrate skin?

One study tested it in people. A 2026 study of 120 healthy volunteers found enhanced skin hydration with creams containing 1% ulvan, a green seaweed polysaccharide, combined with thermal spring water, and scaling was significantly reduced in the ulvan group. Some authors work for a seaweed producer and a cosmetics company. ⁹

Is seaweed safe?

It depends on how it is used. Eating large amounts has been linked to hypothyroidism from excess iodine in a case report. Contaminants are also a concern: in a study of Indonesian seaweed-based food products, lead was found in 50% of samples, arsenic in 35%, cadmium in 25% and mercury in 5%, and a quarter of the contaminated samples exceeded national limits. Allergy to seaweed has been reported. We found no study that measured these risks for seaweed in skincare products. ^{10, 12, 13}

Is fucoidan a proven anti-aging ingredient?

No. A 2026 review says the evidence supports an antioxidant effect of fucoidans, including in skin and wound healing, but that translation is limited by differences in source species, extraction, purification and molecular weight, and that standardized chemistry and better pharmacokinetic data are needed. Two authors work for a fucoidan producer. ⁸

Does Vanu Health make a seaweed claim?

No. This page reports what published studies say. It makes no seaweed, whitening, firming or anti-aging claim about any Vanu Health product.

Keep reading

The Research Desk: every guide and dataset from the same team.
Kelp extract: the ingredient page.
The plump effect: hydration versus structure, and what studies show.
Types of collagen: what each does in skin.
Skin whitening: what studies show on pigment.
The Rise of Blue Beauty: ocean-friendly claims, read closely.

The Rise of Blue Beauty: what skincare washing into the ocean means, and the rules on claims.
Skin Whitening: what the clinical trials show, and the rules in Canada and the US.
The Plump Effect: hydration versus structure in plump-looking skin.
Collagen types: types I, III, IV, VII and XVII in skin.
Notes from the Reef: a book from the Vanu Health library.
Research Desk sources: every reference, organised by guide.
The Research Desk: all guides and datasets.

Sources

Where every claim comes from.

Numbers in brackets link to these entries. Each study was read as its PubMed record, with the title, journal, date and abstract, and study details come from PubMed, the US National Library of Medicine. Links open the paper through its DOI. Dates are those shown on the source.

All sources across the Research Desk are collected, by page, in the master source list.

[1] Marine Drugs (Jesumani and colleagues). Potential use of seaweed bioactive compounds in skincare: a review. December 2019.
[2] Marine Drugs (Kim and colleagues). The beneficial roles of seaweed in atopic dermatitis. December 2024.
[3] Antioxidants (Freitas and colleagues). Highlighting the biological potential of the brown seaweed Fucus spiralis for skin applications. July 2020.
[4] Marine Drugs (Susano and colleagues). Unravelling the dermatological potential of a brown seaweed. February 2021.
[5] Marine Drugs (Nour and colleagues). Eco-friendly extraction of phlorotannins from a brown macroalga abundant in Djibouti: identification related to purification methods towards innovative cosmetic applications. December 2024.
[6] Scientific Reports (Hernández and colleagues). Optimization of ultrasound extraction of phlorotannin-rich extract from Dictyopteris justii with tyrosinase inhibition. February 2026.
[7] 3 Biotech (Xie and colleagues). Quantification of 3,6-anhydro-galactose in red seaweed polysaccharides and their potential skin-whitening activity. April 2020.
[8] Archives of Toxicology (Mangoni and colleagues; two authors are from Marinova Pty Ltd). Therapeutic role of fucoidans against oxidative stress: recent developments, translational challenges, and future directions. October 2026.
[9] Marine Drugs (Ingrez and colleagues; some authors are from a seaweed producer and a cosmetics company). Successful combination of ulvans and thermal spring waters from As Burgas (Ourense) for hydrating cosmetic creams in healthy volunteers. August 2026.
[10] Cureus (Unosawa and colleagues; case report). Hypothyroidism due to seaweed overconsumption. February 2024.
[11] Food Chemistry (Dong and colleagues). Impact of harvesting method and advanced post-harvest processing technologies on the potentially toxic trace elements and iodine content of brown seaweed Alaria esculenta. July 2026.
[12] Italian Journal of Food Safety (Suroto and colleagues). Assessment of chemical, heavy metal, and microbiological contamination of Indonesian seaweed-based food products. April 2026.
[13] Journal of Allergy and Clinical Immunology: In Practice (Thomas and colleagues; letter, abstract not available). Seaweed allergy. November 2018.
[14] Biotechnology Reports (Thong-Olran and colleagues). Seaweed-derived bioactives with anti-tyrosinase activity: a potential for skin-whitening cosmetics. August 2025.

This page is general information from the Vanu Health Research Team. It is not medical advice. The images are AI-generated illustrations, not study images. Last updated October 30, 2026.

The short answer

Sorted by colour, defined by chemistry.

Fucoidan and phlorotannins

3,6-anhydro-galactose polysaccharides

Ulvan