Incest

What is incest?

Incest can be defined as sexual activity with a person from within the immediate family. It is often considered synonymous with intrafamilial sexual abuse,¹ although the broader term 'incest' can include consensual and non-consensual relationships between adults who are related to one another.² The exact relationships which can be construed as incest will vary from culture to culture. Sexual relationships between first-degree relatives are a universal taboo in modern cultures, as are sexual relationships between second-degree relatives. The acceptability of sexual activity, and marriage, between first cousins varies substantially between cultures; in some, it is considered incest and forbidden, whereas in others, it is viewed favourably and encouraged.

One explanation for the near-universal cultural prohibition on incest is the Westermarck hypothesis. First formulated in 1891, this proposes that humans tend to develop a strong sexual aversion to individuals with whom they live closely with during childhood and infancy (usually, siblings and parents). Empirical evidence broadly supports this claim, although the mechanism by which this happens is unclear.³

Many countries have laws that forbid incest but there is considerable variation in the exact nature of these.

In England and Wales the Sexual Offences Act 2003 created an offence of familial sexual abuse (this is covered in Scotland in the 2009 Sexual Offences Act, and in Northern Ireland in the Sexual Offences Order 2008).

The aim of this law was to protect children up to the age of 18 from any form of activity that a person would consider sexual or indecent. The offender may be an adult or another child. It recognises the modern family unit and it defines familial sexual abuse as being between a person and their parent (including adoptive or foster), grandparent, child, grandchild, sibling or half-sibling, uncle, aunt, nephew or niece.⁴

The Sexual Offences Act 2003 also prohibits adult sexual relationships but within a slightly narrower definition that includes just close blood relationships only - parent, grandparent, child, grandchild, older brother, sister, half-brother, half-sister, uncle, aunt, nephew or niece. This prohibition extends to incestuous relationships between consenting adults.

The most common manifestations are sibling incest and father-daughter incest.⁵

How common is incest? (Epidemiology)

Incidence

Sibling sexual abuse is usually recognised as being the most common form of sexual abuse within families.⁶ It has been documented as being five times more common than father/stepfather abuse.⁵ Father-daughter incest was reported by 2.5% of female participants in an anonymous computer-assisted self interview.⁷ One study from Scandinavia looked at all child sexual abuse in one area:⁸

• Girls were victims in 85% of the cases, boys in 12% and boys as well as girls in 3%.

• Sexual penetration had occurred in 53.7% of cases and there was genital or other physical manipulation in 29.6%.

• In 16.7% of cases there was no physical contact but there was some kind of non-contact molestation or exhibitionism.

• Most perpetrators (72%) were well known to the child.

• The most severe violations (regarded as the ones where there was sexual penetration) were significantly more often committed by biological relatives, household members, or family friends than by strangers.

Concerns have been raised that fewer reports of child abuse were made during the COVID pandemic.⁹ Future research will show the impact of the pandemic on family dynamics and intrafamilial abuse.

Currently, there are no reliable data on the prevalence of adult-adult incest, including consensual adult incest.²

Presenting features of incest

See the separate Safeguarding children - How to recognise abuse or a child at risk article.

The offender is reported as male in most cases but female involvement may be under-reported. Although sibling incest is thought to be the most frequently occurring form of incest, the abuse of daughters by fathers or stepfathers is more commonly reported.¹ Abuse by stepfathers is up to five times higher than that by biological fathers. Physical symptoms may include:

• Vaginal pain.

• Rectal pain.

• Vaginal discharge.

• Rectal or vaginal bleeding.

• Chronic dysuria.

• Bedwetting.

• Constipation.

Incest is usually repeated and will often continue for many years. As the daughter reaches an age when she may be able to resist or flee, the activity may be repeated with a younger sister. Though the profiles of incestuous families may vary, the father-perpetrator is typically an immature individual with low self-esteem, while the wife-mother is depressed, helpless or otherwise emotionally absent.¹⁰ The father often uses alcohol to allay his inhibitions before molesting his daughters. Theories have proposed that girls may feel powerless to take active steps to end the abuse for fear of disrupting the family unit.¹¹

Psychological symptoms include:

• Deliberate self-harm.

• Nightmares.

• Sleep disorders.

• Aggressive behaviour.

• Withdrawal.

• Post-traumatic stress disorder.

• Poor concentration.

• Poor performance at school.

• Depression.

• Phobias.

• Eating disorders.

• Precocious sexual behaviour with peers.

Associated factors for incest¹²

When women with children begin new relationships, it may - unintentionally - put their children at greater risk for sexual abuse from new partners. The study by Stroebel et al identified risk factors for father-daughter incest.⁷ In the study, father figures were included within the definition of father-daughter. These risk factors included:

• Parents, where the relationship involved verbal or physical fighting, increased the risk of father-daughter incest five-fold.

• Families where father-daughter nudity was accepted increased the risk.

• Homes with a single-parent mother or where divorce/death of the father resulted in another man living at home, tripled the risk.

• Maternal affection was protective - but the likelihood of being a victim of father-daughter incest was highest if a girl's mother never kissed or hugged her.

According to another survey, if the mother remarries, "the stepdaughters are over eight times more at risk of sexual abuse by the stepfathers who reared them than are daughters reared by their biological fathers".¹³

When considering sibling-associated sexual abuse one study looked at male adolescents who had sexually offended against intrafamilial victims (AIV) and compared them to male adolescents who had sexually offended against extrafamilial victims (AEV). A total of 26 independent samples (8 published and 18 unpublished) that compared a total of 2,169 AIV and 2,852 AEV were analysed.¹⁴

The results of the meta-analysis showed that males who committed AIV presented with greater atypical sexual interests, increased sexual regulation issues, more severe family dysfunction, more extensive childhood maltreatment histories, and greater internalising psychopathology than AEV. Conversely, AEV presented with more indicators of antisociality than AIV.

Other research shows an association between sibling abuse and alcohol consumption.¹⁵

Incest management¹⁶¹⁷

See the separate Safeguarding children - referral and management of an abused or at-risk child article for details as the principles of management are the same.