Algae are very simple, chlorophyll-containing organisms in a family that includes more than 20,000 different known species. A number of species have been used for drugs, where they work as anticoagulants, antibiotics, antihypertensive agents, blood cholesterol reducers, dilatory agents, insecticides, and anti-tumorigenic agents. In cosmetics, algae act as thickening agents, water-binding agents, and antioxidants. Some algae are also potential skin irritants. For example, the phycocyanin present in blue-green algae has been suspected of allergenicity and of causing dermatitis on the basis of patch tests (Source: Current Issues in Molecular Biology, January 2002, pages 1–11).
Other forms of algae, such as Irish moss and carrageenan, contain proteins, vitamin A, sugar, starch, vitamin B1, iron, sodium, phosphorus, magnesium, copper, and calcium. Most of these are beneficial for skin, either as emollients, anti-inflammatory agents, or antioxidants (Sources: European Journa of Dermatology, May-June 2008, pages 303–307; and Journal of Agricultural Food Chemistry, February 2002, pages 840–845). However, the claims that algae can stop or eliminate wrinkling, heal skin, or provide other elaborate benefits are unsubstantiated.
Names of the algae typically found in cosmetics include Ulva lactuca, Ascophyllum, Laminaria longicruris, Laminaria saccharine, Laminaria digitata, Alaria esculenta, various Porphyra species, Chondrus crispus, and Mastocarpus stellatus. It is also listed plainly as "algae extract", though current CTFA (Cosmetics, Toiletries & Fragrance Association) regulations mandate that manufacturers list the specific type of algae each product contains. Algae isn’t a critical ingredient in skin-care products, but does have a positive function; it’s just not the miracle ingredient it’s often made out to be.