The characteristic essential to all paraphilias is the presence of a persistent and/or recurrent, sexually motivated interest that causes harm. This definition has several implications.

Paraphilias can exist even if they have never been acted upon. By definition, all paraphilias begin with a sexual thought and, like non-paraphilic interests, the majority of sexual fantasies are never fulfilled in reality. Sexual acts are only paraphilic if they are motivated by harmful sexual interests. For example, an individual with paedophilia (sexual interest in children) may act on this interest by masturbating while viewing non-pornographic children’s television shows. However, an individual who unintentionally downloads pictures of children from the Internet while meaning to download adult pornography should not be considered paedophilic (even though he or she may still be criminally liable).

Paraphilias are characterized by their persistence. Therefore a single paraphilic thought or activity, especially if it occurs during unusual circumstances, is unlikely to be indicative of a true paraphilia. For example, a woman who while on a vacation and under the influence of alcohol exposes herself once to group of strangers in a bar, would not normally be considered to have exhibitionism (sexual arousal from exposure to strangers). Opportunistic activity that is not sexually motivated, even if it is ongoing, is also exclusionary. A pimp who coerces women to exchange sexual activities for drugs or money, would not meet criteria for sexual sadism even though he repeatedly engages in opportunistic sexual activity with otherwise unwilling participants because, for the pimp, the motivation is financial rather that sexual.

Many sex acts are intimate. Therefore it should come as no surprise that participants can be harmed. Unfortunately whenever sexual activities are considered, ‘harm’ tends to be defined somewhat solipsistically. Paraphilias are characterized by sexual interests or behaviours in which harm is more or less inevitable rather than accidental or random. For example, although sexual intercourse may expose the participants to a number of dangers including sexually transmitted diseases, possibly unintended degrees of intimacy, or subsequent events (e.g. pregnancy), by and large, consensual sexual activity between adults does not inevitably lead to disaster.

In contrast, true paraphilic interests are by definition, harmful. For example, a woman who can only become sexually aroused if she is choked to unconsciousness (asphyxophilia), exposes herself to unintended harm including cerebral anoxia and possible death. The paraphilias associated with crime (e.g. voyeurism, exhibitionism, frotteurism, criminal sadism, and paedophilia) involve non-consensual imposition of sexual activity onto others. Other non-criminal paraphilias (e.g. transvestic fetishism) become problematic when they interfere with the ability to maintain a reciprocal emotional relationship. Most men with transvestic fetishism do not seek therapy and there is no indication they should, unless the interest begins to cause harm. Paraphilic transvestites are sufficiently dependent on cross-dressing that it causes distress. Transvestic fetishism is a good example of a paraphilic condition in which the individual symptoms (wearing women’s clothing while masturbating or engaging in sexual relations) are not problematic. However, when the sexual interest becomes so pervasive that it interferes with consensual sexual relations, a diagnosis is permissible. Transvestic fetishism is very responsive to treatment with selective serotonergic re-uptake inhibitors prescribed at doses low enough to avoid inhibited orgasm.

While paraphilias are characterized by deviant sexual interests, unconventional interests alone are not sufficient to meet criteria for a true paraphilic condition. This is a persistent source of confusion in two specific situations.

Paraphilic interests do not necessarily lead to illegal activities, and vice versa. Therefore, ‘Not all paedophiles are child molesters and not all child molesters are paedophiles’.

With few exceptions, individuals with paraphilic interests not only know they have abnormal sexual interests but also wish they could replace them with ‘normal’ ones. Many confuse fantasy with reality, thinking that illegal sexual interests are equivalent to having committed a sex crime. A major issue in the diagnosis of paraphilic disorders is distinguishing between legal and psychiatric concerns (see Management section below for further details).

In addition to legal issues, clinicians should also consider several other diagnostic issues:

Any discussion of the number of people with paraphilic disorders in the population must begin with a series of caveats. The most important is the fact that the majority of the information available is derived from studies of men convicted of sex crimes. This is a significant problem since not all paraphilias are associated with sex crimes. The problem is compounded by the fact that many paraphilic disorders remain undiagnosed either because assessment was never requested, clinicians did not gather sufficient information, or because the person with the paraphilic disorder was unwilling or unable to disclose the symptoms. Further degrees of confusion and subsequent dispute are added by inconsistent application of existing diagnostic criteria (for example confusing child molesters with paedophiles) or by differing opinions about whether or not to subdivide paraphilic disorders (e.g. diagnosing a person who lures children into sexual activity by exposing to them as a paedophile or as both a paedophile and an exhibitionist). To date, insufficient attention has been paid to the importance of precise definitions of what is being measured, the difference between point and period prevalence, and the potentially significant differences attributable to independent characteristics of the populations being studied. For example, a report on the incidence of ‘sexual sadism’ based on a point prevalence study of sexual assault of women and children in a country in which war is being waged, while important, has little to do with an analysis of the period prevalence of sexual sadism in, for example, North America. There is also an widespread but unwarranted assumption that studies based on criminal populations can be easily generalized to other populations.