A recent theory has been proposed to explain werewolf episodes in Europe in the 18th and 19th centuries. Ergot, which causes a form of foodborne illness, is a fungus that grows in place of rye grains in wet growing seasons after very cold winters. Ergot poisoning usually affects whole towns or at least poor areas of towns and results in hallucinations, mass hysteria and paranoia, as well as convulsions and sometimes death. (LSD can be derived from ergot.)
Ergot poisoning has been proposed as both a cause of an individual believing that he or she is a werewolf and of a whole town believing that they had seen a werewolf. However, this theory is controversial and unsatisfactory. Witchcraft hysteria and legends of animal transformations, as well as hysteria and superstition in general, have existed across the world for all of recorded history. Even if ergot poisoning is found to be an accurate explanation in some cases, it cannot be applied to all instances. An over-reliance on any one theory denies the diversity and complexity of such occurrences.
Some modern researchers have tried to use conditions such as rabies, hypertrichosis (excessive hair growth over the entire body) or porphyria (an enzyme disorder with symptoms including hallucinations and paranoia) as an explanation for werewolf beliefs. Congenital erythropoietic porphyria has clinical features which include photosensitivity (so sufferers only go out at night), hairy hands and face, poorly healing skin, pink urine, and reddish colour to the teeth.
There is also a rare mental disorder called clinical lycanthropy, in which an affected person has a delusional belief that he or she is transforming into another animal, although not always a wolf or werewolf.
Others believe werewolf legends arose as a part of shamanism and totem animals in primitive and nature-based cultures.
The term therianthropy has been adopted to describe a spiritual concept in which the individual believes he or she has the spirit or soul, in whole or in part, of a non-human animal.