Werewolf

A werewolf is a term for a hyloeid (typically human) with one of two physiological conditions causing them to exhibit an appearance and/or behaviour(s) that are associated with non-human animals. Because the genetic predisposition for these conditions are similar or related to psionological mutations, most (if not all) werewolves are possessed of other psionic characteristics.

Etymology
The common name for the creatures is a compound of the old English were "adult male human" + wulf "wolf." Werewolves and other shapeshifters (such as werecats, weretigers/wereleopards in Asian cultures) are also referred to as lycanthropes, from the Ancient Greek λυκάνθρωπος lukánthropos (λύκος lúkos "wolf" + ἄνθρωπος ánthrōpos "human").

Historical context
The common folklore about werewolves did not reach popularity until the Middle Ages, circa the 14th century,; before then there were occasional tales of shape-changers and enchantments, but almost all isolated cases. Most of the extant literature in western and northern Europe came from Germanic traditions. As early as the Viking Age, men were said to become Úlfhéðnar ("wolf-coated men") by wearing the skins of wolves and channeling their spirits to enhance their performance in battle, similar to berserkers that used bear skins. These Germanic werewolves were therefore associated with magic and eventually with witchcraft, leading to the persecution of many in the Christian age who were accused of consorting with animals.

The Germanic tales of werewolves also migrated to the Balkans and the territory of the Slavs and Rus', where descriptions of beast-men became mingled and confused with those of blood-drinkers; thus in Slavic literature werewolves were tied together with vampires, rather than with witches.

Also well-known, though less commonly than the Germanic werewolves, is the ancient Greek tale of King Lycaon. When visited by the god Zeus, Lycaon served him the roasted flesh of his son to see if he was truly omniscient. As punishment for his impudence, Zeus cursed Lycaon and his remaining sons to become wolves; depending on the version of the story told, their sentence was lightened to limit the shape-changing only during the full moon. It is also sometimes said that Lycaon was called by another name until Zeus cursed him, as "lykos" is the Greek word for "wolf."

The Greek historian Herodotus related that the tribe of the Neuri were all transformed into wolves once a year for several days, and then changed back to their human shape.

Folklore and characteristics
Because the nature of werewolves is different when comparing the history and folklore of different world cultures, werewolves are described in contrasting and sometimes utterly opposite ways. Even within a given culture, people often did not agree or were unclear on how a characteristic manifested. For instance, some cultures believed that werewolves were cursed to always be animals, while others believed that they shapeshifted, temporarily, but recurrently. The werewolf might take the literal form of a wolf, or merely become a more bestial-looking man. The werewolf might be conscious and intentional in its animalistic behaviour, or it might be a victim in a trance unaware of what he or she is doing.

Not even the manner of becoming a werewolf is consistent. One might need to be bitten by another werewolf, or merely scratched. One might lay naked in the full moonlight, or sleep under a wolf's skin. Similar to the tale of Lycaon, some believed that engaging in cannibalism or eating any raw flesh would turn one into a werewolf. In religious context, it was believed that committing certain terrible sins brought the wrath of God down in the form of an animal curse.

Acute cutaneous porphyria
Some of the physiological history of both the werewolf myth and the vampire myth can be attributed to a group of rare diseases called porphyrias, in which chemical substances called porphyrins accumulate with high metabolism. The body requires porphyrins to produce heme, which carries oxygen in the blood. But in the porphyrias, there is a deficiency (inherited or acquired) of the enzymes that transform the various porphyrins into others, leading to abnormally high levels of one or more of these substances. This manifests with neurological symptoms or skin problems, or occasionally both.

The porphyric diseases which produce werewolf-like conditions are related to incomplete processing of protoporphyrinogen IX in the body - either because it cannot be formed (a deficiency of coproporphyrinogen oxidase, called hereditary coproporphyria), or because it cannot be converted (a deficiency of protoporphyrinogen oxidase, called variegate porphyria). In both cases the porphyria is described as: Despite the above list of symptoms, for the most part a "werewolf" suffering from porphyria is able to live a relatively normal life without much discomfort or deviation. Werewolfism, as porphyria, is not a constant condition and occurs only in monthly acute episodes which can be predicted; as stated above, the most common environmental stressor is the moon and its phases, called ''lunar synchrony. ''Porphyric attacks cannot be cured but can be treated. Simple at-home care includes taking anti-anxiety medication and keeping cold pressure on the back of the neck. The easiest treatment for the cutaneous symptoms is to maintain high and constant levels of Vitamin D in the diet.
 * acute: primarily affecting the nervous system (characterised by nausea, hypertension, muscle weakness, and occasional short-lived psychiatric symptoms such as anxiety and confusion) and brought on by environmental stressors (in this case correlating with lunar synchrony);
 * hepatic or semihepatic; characterised by neurological attacks (seizures, abdominal pain, psychosis, and/or acute polyneuropathy); and
 * cutaneous; manifesting in skin disease or sensitivity due to the accumulation of porphyrin molecules (which are photoactive) in the skin, causing immediate photosensitivity, vesiculo-erosive skin disease, and/or increased skin fragility and scarring.

Hypophysic Flooding
The behavioural history of the werewolf myth may have some basis in a complication of porphyria called hypophysic flooding. It occurs in people who suffer from porphyria when there is also an underdevelopment of the sellar diaphragm, which covers a cavity in the skull (called the sella turcica) that houses the pituitary gland. The malformation of porphyrins during a porphyric episode can interrupt the normal operation of the sellar diaphragm. When this occurs, fluid in the body may enter the sella turcica and prevent cells called pituicytes from regulating the production of neurohypophysial hormones. These hormones (particularly oxytocin and vasopressin) are then released in quantities higher than normal, leading to behavioural changes such as increased sexual drive and heightened agitation, and physiological changes such as increased muscle density.

Hypertrichosis
Other physical characteristics of the werewolf myth, in particular the animalistic appearance, can be attributed to an extremely rare hereditary or acquired condition called hypertrichosis, or Ambras syndrome (or werewolf syndrome). This condition is characterised almost solely by an abnormal amount of hair growth - over the entire body (generalised) or restricted to a certain area (localised). Hypertrichosis can be either congenital (caused by genetic mutations) or acquired (appearing after birth; causes include the side effects of drugs, associations with cancer, and possible links with eating disorders).

Hypertrichosis has a practically 0% prevalence rate, with only 50 cases of congenital hypertrichosis lanuginosa recorded since the Middle Ages, fewer than 100 cases of congenital generalised hypertrichosis documented by scientific publications and the media (isolated to a single family in Mexico), but with acquired hypertrichosis and hirsutism being more common (hirsutism occurs in about 10% of women between ages 18 and 45).