In communities where they believe in magic and the supernatural, fear of curses and the evil eye can have real psychological effects, sometimes even leading to physical symptoms of illness and malaise1. In the medical world, therefore, the effects fall within the realm of psychosomosis, in particular, the Nocebo Effect. This is an area of neurogenerative disease in which belief and expectation can worsen symptoms2, and within limits, even create symptoms where there's no need for them3.
Although some people believe in curses and intentionally try to enact them upon others - even in the modern world - in most cases those accused of witchery, evil and magic are generally innocent victims, and often already members of disliked minorities or are perceived as an outsider in some way; it is often a case of national development that authorities, scientists and rationalists must convince large numbers of people that it's nonsense before the perceived effects abate.
In face of the evidence of the psyhological nature of curses, believing peoples have had to declare that "Westerners are immune"; for example, the Fang people of Cameroon4 and the Caribs of Dominica5 have both concluded so. But, wrong again - it's not that Westerners are immune - but, that good education6 grants immunity to superstition and makes life more sensible in general, negating the need to explain things in terms of curses and hexes.
Nocebo Effects are negative effects borne from purely psychological factors, causing symptoms where there need be none. It's the negative form of Psychosomosis (the Placebo Effect being the positive form). Nocebo is normally used when a particular perceived threat vector causes distress in a person, which can then cause some kinds of symptoms whether or not the perception of the threat was rational or not. Linked terms such as psychoneurosis, conversion hysteria and somatoform disorders all describe the destructive effect that the mind can have on the body.7,8
Only some physiological symptoms can be made worse by mental states, or induced purely them. They include nausea, headaches, dizziness, skin rashes, breathing difficulties, stomach ulcers, eating disorders and changes in heart rate. Psychoneurosis accounts for 37% of cases of asthma9. Modern fears of things like mobile phone signals are psychosomatic, and in history, so are curses2. Belief can be passed on, in worst-case scenarios becoming psychogenic mass hysteria10.
'Cures' for the nocebo effects are often imagined to be calm reassurance and the presentation of medical facts by someone the sufferer trusts, but, the best long-term preventative measures are a good education, stability at home and general improvements in mental health. Unfortunately these fixes are difficult to attain once things are amiss, but without them it is uncommon that the mere presentation of facts will placate nocebo effects; a variety of social and psychological changes must first occur and the precise combination required is wildly different between individuals.
For more, see:
A purported case from 80 years ago resurfaced in the New Scientist:
“Late one night in a small Alabama cemetery, Vance Vanders [name changed] had a run-in with the local witch doctor [... who] told him he was about to die and that no one could save him. [...] Vanders took to his bed and began to deteriorate. Some weeks later, emaciated and near death, he was admitted to the local hospital, where doctors were unable to find a cause for his symptoms [...]. Only then did his wife tell one of the doctors, Drayton Doherty, of the hex.”
New Scientist (2009)11
The next morning, after much thought, the doctor told the family he had found the witch doctor. He performed another ritual, carefully inspecting his instruments, and administered a drug that made the man sick. He discretely produced a green lizard and pretended it had been secreted by the ill man, " 'Look what has come out of you Vance,' he cried. 'The voodoo curse is lifted.' Vanders did a double take [... and] drifted into a deep sleep. When he woke next day he was alert and ravenous. He quickly regained his strength and was discharged a week later"2.
The cause of the man's illness was his expectation and fear of illness caused by the witch doctor. The clever doctor proscribed an equal but opposite psychological effect. For some time, priests and other representatives of the unknown have been able to change a person's expectations about bodily ills and 'heal' them through suggestion. If the source of the information is given credence, then the effects are pronounced.
The Evil Eye is in many places a strong belief that jealousy and greed lead some people to be able to cast a secret spell on someone else who is better off in some way. Over the short or even over the long term, the victim will suffer from this curse. Anthropologist David Pocock provided detailed reporting on such beliefs amongst the Gujarat caste in North India, where the threat of a najar necessitated permanent vigilance. It is not a mere "belief", but a reality. There is endless, ample evidence. Anyone "can cite hundreds of cases" where a victim has suffered a calamity which follows on clearly from the envy of someone known to them who cast the curse. Take one example who "is distressed because infant has got a bad rash. After a few days of enquiries, this is finally connected to an uncle's visit just after the baby's birth. This uncle had commented on how lively the child was, how he seemed to understand what was happening around him. So the jealous uncle must have cast the evil eye on the precocious child". Anyone in that region can describe "hundreds" of cases. Some people even do it to others without realizing it. Given this scale of "evidence", it is incredibly hard to convince those people that they are deluded, and almost any event can be connected to any person using such antics.1.
Anthony Layng (2010) studied the prevalence of superstitions and witchcraft-accusations amongst the Caribs of Dominica5. The general idea, held by "many tribal and peasant communities all over the world" is that witches are responsible for many social maladies from disease to failed crops, and they are simply evil and sneaky. Often so-called witches are murdered, tortured, expelled or at least shunned; the Dark Ages of Christian history and the heresy-accusations of Islam today both follow(ed) the same psychology. The features of witchcraft highlight the functionalism of religion in wider ways. "Believing that there are witches inclined to harm others with their malevolent power can have numerous social and psychological consequences for a community" says Prof. Layng. Witness how many of the effects serve to reinforce people's already-existing beliefs and to maintain social structure even when the religious dogmas suffer from counter-evidence:
Maintaining mental health (gaining sympathy and compensation for low status, displacing antagonism and jealousy, achieving a sense of control). Victims of witchcraft, often persons who otherwise attract little attention, receive intense sympathetic concern from their neighbours. Those accused of using witchcraft are frequently very unpopular and, therefore, are ideal scapegoats. Blaming misfortune on gods, demons, or bad luck gives the believer very little sense of control; witches, being here among the living, may be identified and dealt with.
Providing Explanations (explaining death, illness, misfortune, and why magical cures sometimes fail). Where witchcraft is presumed, bad luck, accident, or infection are not considered satisfactory explanations. When misfortune is especially persistent, witchcraft is readily assumed to be the cause. When magical cures fail, witchcraft may be blamed for the failure, thus preserving faith in such good magic.
Encouraging proper conduct (reinforcing and clarifying correct behaviour and providing negative role models to discourage bad behaviour). Nonconformists are the most likely to be accused of practicing witchcraft; their strange behaviour provides 'evidence' of their evil nature. [...]
Encouraging generosity and sharing (ensuring an equitable distribution of material resources). In egalitarian societies and communities plagued by persistent poverty, individuals and households adapt by sharing with others. Those who refuse [can be accused of being a witch, or conversely might attract the attention of a jealous witch].
Conserving tradition (defending the social order and community cohesion). Those who openly challenge accepted norms are especially likely to be accused of witchcraft. [...]
Providing entertainment (creating drama and stimulating imagination). Dramatic folktales about witches and gossip concerning an unpopular neighbour suspected of inflicting illness or bad luck on a household are listened to with great interest, especially by children. Consequently, lessons to be learned from these accounts fall on fertile ground and help perpetuate the beliefs.
Coping with rapid social change (attempting to reinstate social order). Under conditions of rapid cultural change and prolonged stress, witchcraft accusations may increase dramatically. Tolerance for deviant behaviour decreases under these conditions, inviting witch hunts and creating incentive to abide by traditional cultural norms. [...]
One hears less about witches once a certain level of economic development has been achieved, but when hard times return, accusations of witchcraft may become common again. For example, there has been a resurgence of this belief in sub-Saharan Africa in recent years. [...]
Some of the methods used subconsciously by believers to defend their beliefs are typical. When traditional remedies fail (or in modern monotheistic religions, when prayer fails) it is often said that lack-of-genuine-belief is the cause. The ironic solution to failure of traditional solutions is therefore is to believe more strongly!
Layng has led us on to the discussion of religion in general; see: What Causes Religion and Superstitions?.
Because of the wide variety of its purposes and uses, belief in witchcraft, curses, hexes and other sneaky supernatural slingshots can be difficult to dispel. But once dispelled, it becomes clear that the cause of psychological all along. When exposed to arguments, or evidence, that curses don't work, belief systems can often adapt to circumvent the facts.
Well-educated folk from developed countries rarely believe in witchcraft. Their societies do not use curses to explain ailments, and, there's no need to do so. The true biological and psychological causes of disease are understood too well. Curses don't have the required effect on such people: there's no serious or negative expectation resulting from the curse, therefore, psychogenic symptoms are not generated.
Superstitious peoples rarely come to the conclusion that their community is wrong; the normal reaction is to declare that "Westerners" are immune. One researcher documented this reaction amongst the Fang people of Cameroon4, and the same for the Caribs of Dominica5.
But it's not that Westerners are immune - rather, that good education grants immunity to superstition and makes life more sensible in general.