What is it?
A brown seaweed, Ascophyllum nodosum, also called knotted wrack or rockweed, that grows in the tidal waters of the North Atlantic. It contains alginic acid, mannitol, laminarans and fucoidans, along with minerals such as potassium and, like other brown seaweeds, iodine. In cosmetics the seaweed itself, or a powder or extract made from it, is used as a skin-conditioning ingredient.
Key information
- The CIR Expert Panel concluded in 2019 that Ascophyllum Nodosum and its extract and powder are safe in cosmetics as currently used.
- Human tests of Ascophyllum nodosum extract at 0.5 to 75 percent found no skin sensitization.
- Like other seaweeds, knotted wrack can take up arsenic and heavy metals from seawater, so manufacturers are expected to limit these impurities.
- France has authorized knotted wrack for use as a vegetable and condiment.
More information
Knotted wrack is a large brown seaweed, up to 3 meters long, that grows along North Atlantic coasts from Virginia to Spain. For cosmetics it is used whole, dried and ground into a powder, or extracted; one extract described to the Cosmetic Ingredient Review (CIR) was made by grinding the seaweed, extracting it with water and purifying it by filtration. Knotted wrack is among the seaweeds France has authorized as vegetables and condiments.
In 2019 the CIR Expert Panel reviewed 82 brown algae ingredients and concluded that 68 of them, including Ascophyllum Nodosum, Ascophyllum Nodosum Extract and Ascophyllum Nodosum Powder, are safe in cosmetics in the present practices of use and concentration; the other 14 lacked enough data. Ascophyllum nodosum extract did not cause sensitization in human tests at 0.5 to 75 percent or in guinea pigs, was not irritating to rabbit skin, and was mildly irritating to rabbit eyes. The seaweed was not toxic when fed to pigs at up to 10 percent of their feed for 23 days or to rats at up to 15 percent for 4 weeks. According to 2019 FDA data, Ascophyllum Nodosum Extract was used in 140 cosmetic products.
The Panel noted that brown algae can contain arsenic, heavy metals and pesticide residues and asked manufacturers to use good manufacturing practices to limit them. It also noted that brown seaweed taken as a dietary supplement can deliver a lot of iodine, but said iodine exposure from cosmetics would be far less than from eating it.
On labels look for Ascophyllum Nodosum, Ascophyllum Nodosum Extract or Ascophyllum Nodosum Powder, sometimes with “(Seaweed)” added.
Sources: CIR: Safety Assessment of Brown Algae-Derived Ingredients as Used in Cosmetics (final report, 2019); Life (2024): Seaweed nutritional value and bioactive properties: insights from Ascophyllum nodosum, Palmaria palmata, and Chondrus crispus
