Scytonemin is a biological pigment synthesized by many strains of cyanobacteria, including Calothrix sp., Lyngbya aestuarii, and others. It was originally discovered in 1849, although the structure remained unsolved until 1993. Scytonemin is believed to act as a bacterial sunscreen with a broad absorption from 325-425 nm and a separate maxima at 250 nm, and its biosynthesis triggered by exposure to UV light.