Is nostoc harmful?

Nostoc itself is generally not harmful to humans or animals. However, some species of Nostoc can produce toxins under certain conditions, which may pose a risk, particularly in aquatic environments. In these cases, nostoc can cause health problems if ingested or if exposed to the toxins in large amounts. For most situations, nostoc is considered relatively harmless, though precautions should be taken when handling it due to the potential for skin irritation.