Natural substances are biologically active components produced by organisms. So far, they have been of interest to researchers primarily as the basis for medicines, because some natural substances have been shown to inhibit tumor growth or have antiviral or antibacterial effects. Natural substances are also produced by organisms in order to better cope with their environment. For example, some lichen species produce the orange pigment parietin to protect themselves against UV radiation. However, most of the functions of the natural substances discovered so far are still completely unknown.