Hexakosioihexekontahexaphobia is the fear of the number 666. Some definitions classify it as any kind of fear, superstition, or aversion to the number, but as a "phobia," the term usually refers to an extreme fear that causes intense anxiety and discomfort, and is characterized by extensive efforts aimed at avoiding any contact with the number. An individual with hexakosioihexekontahexaphobia may, for instance, refuse to live at a house with 666 in the address, be made uncomfortable by or entirely avoid the 666th page of a book, or take pains to ensure that he is never in a situation wherein he must pay $6.66 for anything. This phobia originates in the Biblical book of Revelations, in which 666 is identified as the mark of the beast, alternatively identified as Satan, the Antichrist, the Roman emperor Nero, or a variety of other entities.
Most cases of hexakosioihexekontahexaphobia are closely linked to the Biblical use of the number 666. Individuals with the phobia tend to believe that any use of 666 is somehow evil and may even be connected to negative consequences in this life or in another. An individual who suffers from hexakosioihexekontahexaphobia may possess the irrational belief, for instance, that the number itself somehow invokes Satan or one of the other entities that it purportedly represents. It is possible for one to possess a phobia of the number 666 without associating it with any religious meaning, but this is very rare.
Individual responses to the number 666 vary substantially based on whether one is merely superstitious or actually has an ingrained psychological phobia of the number. A merely superstitious individual may try to avoid the number when it is convenient to do so, but he is unlikely to take any great pains to do so. One with a genuine case of hexakosioihexekontahexaphobia, on the other hand, will likely notice the number throughout his surroundings, perhaps even in veiled or coded forms, and will take every pain to avoid it. Failure to avoid the number often leads to intense anxiety, discomfort, and dread.
In some cases, it is possible to treat hexakosioihexekontahexaphobia, or at least to dramatically decrease the deleterious effects of observing the number 666. Therapy and some forms of medication can be used to treat a variety of phobias and may be effective with hexakosioihexekontahexaphobia as well. Some individuals may benefit more from discussion with a church authority who can explain the history and meaning of the number. This can help an individual with hexakosioihexekontahexaphobia to see that, as a number or a symbol, 666 has no power in and of itself to do any form of harm.