It's become a staple of the horror film genre, regarded with deep uneasiness by many Christians involved in healing and deliverance ministries and with deep glee by retailers. Depending on your point of view, the Ouija board is either a portal to the dark dimensions or a harmless parlour game.

Every so often, it hits the headlines again. This time round it's thanks to internet search giant Google, which released figures about search trends leading up to the notorious Black Friday, which sees billions spent in store and on line in a single day. A throwaway sentence in the release remarks that thanks to the just-out eponymous horror film, searches for Ouija boards are up by 300 per cent since October. It's evidently the must-buy Christmas present this year.

But what exactly is it, and should we be worried?

Essentially, it's a board marked with the letters of the alphabet, the numbers one to nine, "Yes" and "No" and sometimes "Hello" and "Goodbye". Participants place their hands on a planchette - a small piece of wood or plastic - or a glass, which moves to different locations and spells out words. Ouija is actually a trademark, and was not regarded as having a particularly spiritual significance until it was popularised by the medium Pearl Curran during the First World War; the terrible death toll of the war led to an interest in all sorts of spiritualist phenomena.

According to a Smithsonian article, it was the 1973 film The Exorcist which really made ouija scary, though reports of its bad effects had surfaced from time to time. For instance, in 1921 The New York Times reported that a Chicago woman sent to a psychiatric hospital tried to explain to doctors that ouija spirits had told her to leave her mother's dead body in the living room for 15 days before burying her in the back garden. In 1930 there were reports of two women in New York who had murdered another, supposedly encouraged by ouija boad messages. However, it was The Exorcist, with its disturbing picture of a young girl possessed by an evil spirit, that set alarm bells ringing in the Christian community. It happened to coincide with the rise of the charismatic movement with its focus on supernatural gifts and the reality of the spiritual world, and its sense that the Church really was in conflict with the powers of darkness.

However, Christian opposition to it, from whatever point on the theological spectrum, has been rock-solid. Darren Gallagher, a spokesman for Ellel Ministries, which counts healing and deliverance among its activities, told Christian Today that Ouija boards were "an attempt for those who are living to contact the dead to gain an understanding of the future". "The fact that people's intention is to contact the spiritual realm outside the blessings and parameters that God has set out could lead to them to connect with the evil spiritual realm," he says. "Therefore such things as Ouija boards are not just harmless fun but could potentially be spiritually dangerous for those who take part in such things." Gallagher points out that the New Testament believers "gathered together their occultic objects and burnt them because they knew that these practices were not compatible with their new life in Christ".

Linda Stalley, a co-leader of the Maranatha healing and renewal community, also sounded a warning. She tells Christian Today that it is far from innocent fun. "I've talked with many people who have been very afraid because something has happened beyond explanation," she says. "It has been trivialised – one of the devil's most helpful tools. We should take it very seriously."

She adds: "The Bible warns us about communing with spirits. Any deliberate consultation with spirits other than with God's Spirit is damaging."

As an example of this "damage", she says: "In my experience the most common consequence is that there is an obstruction - people do want to seek God, but there is a silence: God is not communicating with them. They feel they have lost contact with God, there is a blank space. There is spiritual depression and oppression; there is a cloud hanging over them."

But is it really the case that people who use Ouija and other 'spirit boards' are contacting supernatural beings? Certainly, there is often some sort of communication, with intelligible words and sentences spelt out without the apparent volition of the participants. It is far from clear, though, that there is anything supernatural at work. As long ago as 1852, William Carpenter identified what he called the "ideomotor" effect, in which muscular activity could take place without the will of the conscious mind. The following year the scientist Michael Faraday conducted an experiment targeted at another Victorian spiritualist fad, table-turning, which demonstrated the same principle: a thought or reaction can cause an infinitessimally small physical response which is amplified through an appropriate physical object, such as a pendulum or a planchette, to create an observable physical effect.

The physical cause of the movement of a planchette or glass, then, is very well understood: it's the unconscious or barely-conscious wishes of the participants which are steering it in a particular direction – and Linda Stalley, for instance, who is deeply concerned about the spiritual effects of Ouija, is entirely comfortable with this explanation of the mechanics: "Scientists can explain the mechanism, but not the origin," she says. "It's not either-or." However, that may not be all there is to it.

Rt Rev Dominic Walker, now retired but serving as an honorary assistant bishop in Swansea and Brecon, served as co-chair of the Christian Deliverance Study Group and is the author of The Ministry of Deliverance. Discounting trickery, he says, there are two theories about what is going on.

"The first is that the 'players' are in contact with a spirit who is giving them a message. Some would say that this is dangerous because people cannot know if they are in contact with a good or evil spirit or even an evil spirit masquerading as a good spirit. Christians have traditionally sought to receive spiritual guidance through prayer to the Holy Spirit and through the prayerful reading of scripture or the Ignatian spiritual exercises involving imaginative contemplation.

"The second theory is that one or more of the 'players' is creating some kind of psychic energy that is making the glass move and the message being spelt out is something from the unconscious mind. This again is dangerous because in therapy or counselling there would be someone to assist with looking at such material and ensuring that it does not overwhelm the person."

His own view, he says, "tends towards the latter explanation", because "the 'messages' often reflect how someone is feeling deep within themselves and sometimes this has had a damaging effect".

So the spike in Ouija boards' popularity, he says, is "an alarming trend, because what might be seen as a bit of fun might well have tragic consequences".

So here, the two explanations seem to converge. It isn't necessary to posit an actual evil spirit manipulating the board, or indeed the spirit of someone deceased - and this might in any case be giving rather too much ground away to the spiritualist movement, which takes a particular view of these things. However, whatever predispositions we bring to this, we can very easily understand how bringing deeply hidden and repressed feelings and desires to the surface through a 'game' might be damaging.

Ouija boards may not be quite strong enough to bear all the weight of fear with which some Christians view them, and we need to be careful not to fall into superstition. However, there are enough wise voices counselling against their use to make us very wary of involvement with them – and as Dominic Walker implies, why would we bother? After all, we have prayer, the Scriptures and the Holy Spirit.