Mycosporine-Like Amino Acids: Algae's Natural Sunscreen
Shinorine and porphyra-334 are the two mycosporine-like amino acids packed into the fronds of Porphyra, the red alga pressed into nori sheets. Both absorb ultraviolet light with a peak at 334 nanometers, inside the UV-A band. They are how a plant that photosynthesizes at the tide line keeps its own DNA intact under full sun, and they are the chemistry behind Helioguard 365, one of the few commercial skincare actives built from these molecules.
Mycosporine-like amino acids (MAAs) are small, water-soluble compounds, most under 400 daltons, built around a cyclohexenone or cyclohexenimine ring with an amino acid side chain. More than 20 are well characterized, and every one absorbs ultraviolet light somewhere between 309 and 362 nanometers. A 2011 review in Marine Drugs described them as the strongest natural UV-A absorbers known. When a molecule captures a photon, it releases more than 90% of that energy as heat, which is why MAAs stay photostable through hours of exposure.
What Are Mycosporine-Like Amino Acids?
The ring does the absorbing. The amino acid side chain tunes where the peak lands:
- Mycosporine-glycine: 310 nm, UV-B
- Palythine: 320 nm, UV-B to short UV-A
- Shinorine and porphyra-334: 334 nm, UV-A
- Palythene: 360 nm, long UV-A
That spread matters because no single filter covers the whole ultraviolet range. MAAs are no exception, which is why algae typically hold several at once.
Their photodecomposition quantum yields are tiny, between 1.2 x 10⁻⁵ for palythine and 3.4 x 10⁻⁴ for shinorine in aqueous solution. Sunlight that fragments a labile organic filter leaves an MAA largely intact, a durability advantage formulators have noticed.
An Algae Sunscreen Ingredient Built for UV-A and UV-B
A 2020 survey in Marine Drugs found MAAs in 572 species of algae: 486 red, 45 green, and 41 brown. The algae sunscreen ingredient framing is chemically accurate. Your sushi wrapper alone carries two of the compounds.
The gap is concentration. Inside the seaweed, MAAs accumulate to levels that screen real sunlight. On skin, commercial products deliver a fraction of that, and the algae story starts to blur.
Mycosporine Coral Symbiosis: Sunscreen, Shared
Corals cannot make MAAs. The biosynthetic machinery traces back to cyanobacteria, and reef animals obtain the compounds through symbiosis. Symbiodiniaceae, the dinoflagellates living inside coral tissue, carry a conserved gene cluster for MAA biosynthesis. Genome work by Shoguchi at the Okinawa Institute of Science and Technology suggests that roughly half of Symbiodiniaceae lineages can synthesize MAAs, and that the cluster has moved between lineages by horizontal gene transfer.
That is mycosporine coral symbiosis in one line: the animal provides shelter, the symbiont provides sunscreen. When a coral bleaches and expels its symbionts, it loses that supply. The same review proposed that bleaching tolerance may be reinforced by MAAs coming from both the dinoflagellates and the coral itself.
The Cyanobacteria UV Filter Connection
The first genetic map of MAA production came from a cyanobacterium. In 2010, Balskus and Walsh published the sunscreen biosynthetic pathway of Anabaena variabilis in Science, identifying the enzymes that assemble the ring from shikimate-pathway precursors. That work turned the cyanobacteria UV filter from a natural curiosity into a manufacturing blueprint. Instead of harvesting red algae, researchers can express the pathway in engineered microbes, the most plausible route to the cost cuts the ingredient needs.
Natural UV Protection Skincare: What the Data Shows
The strongest skin data comes from palythine, an MAA extracted from the red alga Chondrus yendoi. In a 2017 study in the British Journal of Dermatology, King’s College London researchers exposed human keratinocytes to solar-simulated radiation. Palythine at just 0.3% cut UV-induced cell death, cyclobutane pyrimidine dimers, and oxidised DNA bases, and suppressed inflammatory and photoageing markers. It kept more than 95% of its UV absorbance after 40 standard erythema doses, and it showed antioxidant activity even when added after exposure.
The catch is spectrum. At 10%, palythine reached an SPF of 17.9 but a UV-A protection factor of only 1.6. These uv absorbing compounds are strong in UV-B and short UV-A, then fall away quickly. A single MAA is not a complete filter on skin.
Where MAAs Stand on a Label
No MAA is an approved UV filter in the United States, where sunscreens are regulated as drugs, or in the European Union, where filters are approved individually under Annex VI of the Cosmetics Regulation. Helioguard 365, the Mibelle ingredient made from Porphyra umbilicalis (porphyra-334 and shinorine at an 11.5:1 ratio), is sold as a protective antioxidant active, not as a filter that counts toward your SPF. Mibelle’s own clinical test used a cream with 5% Helioguard 365, which delivered a final MAA concentration of roughly 0.005%.
Treat MAA products the way you would any extract active. They can work as antioxidants with a UV-A assist. They are not yet sunscreens. If you want approved protection, the mineral filters still carry the load, and you can compare the options in our zinc oxide UV protection guide or alongside ectoin, another microbial stress molecule that made the jump to skincare. Algae’s role in beauty extends well beyond UV, as our algae oil guide shows.
The molecule is real, the absorption is real, and the coral that shares its sunscreen shows that nature solved this problem first. The remaining gaps are formulation and honest labeling.