Scytonemin is a secondary metabolite and an extracellular matrix (sheath) pigment synthesized by many strains of cyanobacteria, including Nostoc, Scytonema, Calothrix, Lyngbya, Rivularia, Chlorogloeopsis, and Hyella.

[1] Scytonemin-synthesizing cyanobacteria often inhabit highly insolated terrestrial, freshwater and coastal environments such as deserts, semideserts, rocks, cliffs, marine intertidal flats, and hot springs.

[2] The pigment was originally discovered in 1849 by Swiss botanist Carl Nägeli,[3] although the structure remained unsolved until 1993.

[4] It is an aromatic indole alkaloid built from two identical condensation products of tryptophanyl- and tyrosyl-derived subunits linked through a carbon-carbon bond.

[10] This effect is due to the dissipation of the absorbed photons by the scytonemin molecules into heat.