The edibility and safety of every lichen that is currently known haven’t been tested. Therefore, people should avoid eating lichens unless they are confident that the type they want to eat is edible and not poisonous and unless they can identify it correctly. It’s best to assume that all lichens are harmful when eaten unless there is no doubt that a particular kind is safe.
Lichens containing significant quantities of vulpinic acid are thought to be toxic to humans. Two lichens in this category are the wolf lichen (Letharia vulpina) and the tortured horsehair lichen (Bryoria tortuosa). There may be many more lichens in the poisonous category. On the other hand, only a few lichens may be harmful when eaten. Researchers don’t yet know which of these scenarios is true.