Algae are very simple, chlorophyll-containing organisms in a family that includes more than 20,000 different known species. 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. 
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, as emollients, anti-inflammatory agents, or antioxidants. [2, 3] However, claims that algae can stop or eliminate wrinkling, heal skin, or provide other elaborate benefits are unsubstantiated.
Algae is not a critical ingredient in skin-care products. Although it does have a positive function, it isn’t the miracle ingredient it’s often made out to be.
- Neilan B. The molecular evolution and DNA profiling of toxic cyanobacteria.. Curr Issues Mol Biol.. 2002;4(1):1-11.
- Shih M, Cherng J. Potential protective effect of fresh grown unicellular green algae component (resilient factor) against PMA- and UVB-induced MMP1 expression in skin fibroblasts.. Eur J Dermatol.. 2008;18(3):303-7.
- Rupérez P, Ahrazem O, Leal J. Potential Antioxidant Capacity of Sulfated Polysaccharides from the Edible Marine Brown Seaweed Fucus vesiculosus.. J Agric Food Chem.. 2002;50(4):840-5.