We did our research and gathered some interesting facts on how common incest is: its history, its types, risk factors, and psychological harms. Read on:
Sex is one of the most powerful and formative aspects of the human experience. While it can be empowering and euphoric under the right circumstances, it can also be devastating and painful under the wrong ones.
That’s why most of us tend to keep sex outside of the family. Family members who engage in sexual activity with each other are committing an act called incest, and in most cases, it’s nonconsensual and psychologically scarring.
We did our research and compiled a wealth of data on the prevalence, laws, history, and effects of incest.
Table of Contents
Here are some highlights from the available data on incest:
- Stepdaughters are over 8 times more at risk of sexual abuse by stepfathers than by biological fathers.
- Incest is legal between consenting adults in the states of New Jersey and Rhode Island, but marriage is illegal.
- Colorado has the highest maximum fine for incest of any state – $750,000, in addition to 2 to 12 years in prison.
- In one study, 93% of women who had been incestually abused by their fathers developed eating disorders. 100% experienced depression.
- Single-mother families with another man living in the home (not the father) are three times more at risk for father-daughter incest.
- Mother-son incest is the least common type of incest reported.
What Is Incest?
You’ve probably heard of incest, but it may be a little different than you think. While the term incest might invoke images of redneck weddings or goofy stepfamily porn, in most cases, it’s much more serious than that.
In most cases, incest involves the abuse of children or other family members.
- Incest – also called intrafamilial sexual abuse – is defined as sexual activity with a person in one’s immediate family. (Patient, 2022)1
- In simple terms, incest is sexual activity between family or close relatives. This typically includes blood-related people but can include relations from marriage, stepfamily, adoption, or lineage. (RAINN, 2009)2
- Incest is a common form of child sexual abuse. Most instances occur between older male relatives and younger female children in families of all demographics. (Feminist, 1998)3
How Common Is Incest?
One of the most difficult things to determine about incest is how often it actually occurs. Not every victim is willing to report their abuse, and results vary wildly depending on region and culture.
Here’s the best data we have on the prevalence of incest worldwide:
- The prevalence of child sexual abuse (not always incestual) is difficult to determine, and one study found it was between 6 and 62% for female children. (Zeitschrift fur Klinische Psychologie, Psychopathologie, und Psychotherapie, 1991)4
- The prevalence of abuse depends on the definition. The broadest terms include extra-familial child sexual abuse (no incest), sexual abuse with or without physical contact, with or without violence, etc.
- Depending on culture, source of reporting, and location, the results of studies on the prevalence of incest range from 5% to 62%. (Medical Science Monitor, 2014)5
- One study found that the most common type of incest is father-daughter (34.9% of all incest), followed by brother-sister (14%). (Medical Science Monitor, 2014)5
- 75% of perpetrators in the study were blood relatives (consanguineous), and 25% were not (stepfamily, adopted family, etc.).
- Mother-son incest was the least common type reported.
- One study of 296 incest cases involving father-daughter incest had the following results: (Medical Science Monitor, 2014)5
- 70 perpetrators were biological fathers of the victim.
- 87 were biological relatives such as grandfathers, brothers, sisters, or cousins.
- 73 were stepfathers.
- 1.8% of female high school students in Istanbul, Turkey, reported being victims of incest. (Child Abuse & Neglect, 2006)6
- One study found that sibling sexual abuse (SSA) is the most common form of sexual abuse within families. (Frontiers in Psychiatry, 2022)7
- SSA has been reported to be five times more common than father or stepfather abuse. (Patient, 2022)1
- One study found that the prevalence of intrafamilial (incestual) child sexual abuse was 18% for girls and 8% for boys. (Evolutionary Psychology, 2019)8
- One study pulled data from 217 publications and millions of participants; it estimated that overall, self-reported studies had a child sexual abuse prevalence of 127 per 1000 cases (12.7%), and informant studies had a prevalence of 4 per 1000 cases (0.04%). (Child Maltreatment, 2011)9
- Self-reported child sexual abuse was more common for females (18%) than for males (7.6%).
- Asia had the lowest rates of child sexual abuse for both boys and girls. The highest rates for girls were in Australia (21.5%), and the highest rates for boys were in Africa (19.3%).
- This study is not specific to incestual child sexual abuse; while many instances in the study are incestual, some are not.
- Grenada noticed an increase in incest in 2020. From January to December 2018, they had 6 cases. During the same period in 2019, there 8 cases. As of September 2020, there were 56 incest cases. (Now Grenada, 2020)10
- Sexual offenses increased overall during the Covid-19 lockdown period.
- Police officials in Grenada expressed serious concern about the prevalence of incestual abuse toward children aged 13 to 16.
- One Swedish study looked at all child abuse in a specific area over a period of years and found the following data: (Archives of Sexual Behavior, 2001)11
- 85% of victims were girls, 12% were boys, and 3% involved boys and girls.
- Sexual penetration occurred in 54.5% of cases.
- 72% of perpetrators were well known to the child (i.e., relatives, family friends, etc.)
- Biological relatives, family friends, or household members are significantly more likely to commit severe violations (sexual penetrations) than strangers.
History of Incest
While pre-historic humans may have found incest necessary for reproduction in some cases, the agricultural revolution and gravitation toward permanent settlement rendered the practice obsolete.
Here’s a look at some of the incestual trends throughout history:
- 45,000 years ago, humans lived in communities so small that it was difficult to find someone to reproduce with who was not a relative. (History of Yesterday, 2021)12
- In a study of the genetic makeup of 1,785 ancient humans, only 1 was found to have first-degree relatives (siblings or parent-child) for parents. (Nature Communications, 2021)13
- 54 of the ancient humans (3%) were the products of first-cousin or second-cousin parents.
- The royal families of ancient Egypt, Peru (Inca), and Hawaii engaged in incest to some extent. (The Journal of Sex Research, 1982)14
- Ancient China did not allow first cousins with the same surnames to marry; however, first cousins with different surnames could marry. (Sexual Life in Ancient China, 1974)15
- Several Egyptian kings married their own siblings (Oxford University Press, 1983)16:
- Arsinoe II married her younger brother, becoming the first in the Ptolemaic royal family to have a full-sibling marriage.
- Tutankhamun married his half-sister and was himself a child of incest.
- The Ptolemaic royal family was known for incest. For example, Cleopatra VII married two of her younger brothers, and her parents were also siblings.
- Greek law allowed marriage between siblings if they had different mothers. (Hellenic World Encyclopaedia, 2006)17
- In the first two centuries A.D., commoners in Roman Egypt engaged in brother-sister marriages frequently. (The Journal of Sex Research, 1982)14
Incest in the U.S.
Incest in the U.S. seems to have been largely overlooked as a problem before the 1980s. Incest is very closely tied to child sexual abuse, and most of the data on both subjects only comes from the past few decades.
These data points highlight the extent of the incest problem in America:
- In 1975, one text asserted that the rate of father-daughter incest in the U.S. was as low as 1 in a million families. Further research, however, revealed that it was much more common. (Psychiatric Times, 2011)18
- By 1986, another source estimated that father-daughter incest was as common as 1 in 20 families with a biological father and 1 in 7 families with a stepfather.
- Studies indicate that 160,000 women per million in the U.S. have been incestuously abused as children, and 45,000 per million were victimized by their fathers. (U.S. Department of Justice, 1986)19
- One study estimates that over 90% of all childhood sexual abuse is perpetrated by family members, friends of the family, or other people that children know closely. (Medium, 2020)20
- Data suggest that 1 in 3 girls, and 1 in 7 boys, are sexually abused before they turn 18 in the U.S. (Journal of Spiritual Formation & Soul Care, 2009)21
- 14% of these victims are under the age of 6.
- 80% of these victims are incestually abused by family members, while 19% are abused by trusted adults.
- Men are far more reluctant to admit abuse than women, so the percentage of abused boys may be much higher.
- Other studies estimate child sexual abuse may be as common as 54% of girls and 16% of boys.
Types of Incest
There are different types of incest depending on the family members who perpetrate it. While there is consensual incest between related adults, most of it occurs when one or both individuals involved are underage.
Here’s a breakdown of the different types of incest and their characteristics:
- The most commonly reported form of incest is between adults and children. This is known as child incestuous abuse. (Rutgers School of Social Work, 2014)22
- One study of adult women in San Franciso found that about 17% had been abused by stepfathers and 2% by biological fathers.
- The National Center for Victims of Crime reports that a staggering portion of rapes in the U.S. are perpetrated by a family member:
- 46% of children who are raped are victims of family members.
- 61% of American rape victims are raped before the age of 18.
- 29% of all rapes occurred when the victim was under age 11.
- 11% of rape victims are raped by fathers or stepfathers; 16% are raped by other relatives.
- Sibling abusive incest happens commonly in families where one or both parents are either absent or emotionally unavailable. Incest is used by one sibling to assert power over the other. (Psychology Today, 1993)23
- Absent fathers are a significant factor in cases where a female child is sexually abused by a brother.
- One study of 62 female incest victims found that 23% were sexually abused by a brother, and about 24% were abused by a father. (Child Abuse & Neglect, 1999)24
- 100% of brother-abused and father-abused women experienced depression.
- About half of the women of brother-abused (56%) and father-abused (50%) struggled with substance abuse.
- 93% of father-abused women had eating disorders, compared to 80% of sibling-abused women.
- Some parts of the world consider relationships between first cousins to be incestual, while other parts tolerate it. (Paediatrics and Child Health, 2008)25
- First and second-cousin marriages are less than 1% of all marriages in Western Europe, North America, and Oceania.
- They are about 9% of all marriages in South America, East Asia, and Southern Europe.
- They’re about 50% of all marriages in the Middle East, North Africa, and South Asia.
- First and second-cousin marriages are less than 1% of all marriages in Western Europe, North America, and Oceania.
Risk Factors for Incest
Certain factors have been shown to increase the risk of incest in families. One of the most troubling risk factors is generational abuse. When perpetrators go unpunished, and victims go untreated, incest is likely to continue in a family through generations.
The highest risk factor comes from unrelated fathers. Single mothers should never, ever invite a man to live at home with their daughter until they are absolutely sure he does not have abusive intentions.
Here’s a look at the most prevalent risk factors for incest.
- Stepdaughters are over 8 times more at risk of sexual abuse by stepfathers than by biological fathers. (Patient, 2022)1
- Disturbed family relationships create a shift in expectations or responsibilities that can lead to incest. (Postgraduate Medicine, 1998)26
- Lack of spousal sexual activity commonly precedes incest.
- Fathers (both biological and step) who sexually abuse their daughters are only 34% likely to be present in the home during the daughter’s early childhood, compared to 70% for non-abusive fathers. (Evolutionary Psychology, 2019)8
- Some studies suggest that incest “runs in families,” as incestual offenders are likely to have been sexually abused as children. (Clinical Psychology Review, 2015)27
- Risk factors for father-daughter incest include the following: (Patient, 2022)1
- Families with parents who engage in verbal or physical fighting are five times more at risk of father-daughter incest.
- Families with accepted father-daughter nudity are at increased risk.
- Singe-mother families with another man living in the home (not the father) triple the risk of father-daughter incest.
- The likelihood of father-daughter incest increases if a girl’s mother never or rarely hugs, kisses, or shows affection toward her.
Incest and the Law
Incest is, predictably, illegal in all U.S. states when a child is involved and illegal in most states between adults.
That being said, the laws and punishments vary by state. Here’s the data:
- Incest is illegal in the majority of U.S. states, but punishments vary. (World Population Review, 2022)28
- New Jersey and Rhode Island have legal incest so long as it occurs between adults. Marriage, however, is illegal.
- Here’s a breakdown of incest laws by state in the U.S., including the prison sentences and applicable fines: (World Population Review, 2022)28
- New Jersey – 18 months to over 15 years
- Rhode Island – No criminal prosecution for 16+
- Alabama – 1 to 10 years up to / $15,000
- Alaska – 2 to 12 years up to / $50,000
- Arizona – 1 to 3.75 years
- Arkansas – 3 to 10 years / $10,000
- California – up to 3 years / $10,000
- Colorado – 2 to 12 years / up to $750,000
- Connecticut – 1 to 5 years / $5,000
- Delaware – up to 1 year / $2,300
- Florida – up to 15 years / $5,000
- Georgia – 10 to 30 years
- Hawaii – up to 5 years
- Idaho – up to a life sentence
- Illinois – 2 to 10 years / $25,000
- Indiana – 1 to 6 years
- Iowa – up to 5 years / $7,500
- Kansas – 5 to 136 months
- Kentucky – 5 years to life
- Louisiana – 5 to 30 years
- Maine – up to 5 years / $5,000
- Maryland – 1 to 10 years
- Massachusetts – up to 20 years
- Michigan – up to 2 years / $500
- Minnesota – up to 10 years
- Mississippi – up to 10 years / $500
- Missouri – up to 7 years
- Montana – up to a life sentence
- Nebraska – 1 to 25 years
- Nevada – 2 years to life / $10,000
- New Hampshire – 10 to 20 years
- New Mexico – up to 3 years / $5,000
- New York – 10 to 25 years
- North Carolina – 10 to 182 months
- North Dakota – up to 5 years / $10,000
- Ohio – 2 to 6 years
- Oklahoma – up to 10 years
- Oregon – up to 20 years / $375,000
- Pennsylvania – up to 10 years
- South Carolina – 6 months to 5 years / minimum $500
- South Dakota – up to 15 years / $30,000
- Tennessee – 3 to 15 years up to / $10,000
- Texas – 2 to 20 years up to / $10,000
- Utah – up to 5 years / $5,000
- Vermont – up to 5 years / $1,000
- Virginia – 1 to 20 years / up to $100,000
- Washington – up to 10 years / up to $10,000
- West Virginia – 5 to 15 years / $500 to $5,000
- Wisconsin – up to 40 years / $100,000
- Wyoming – up to 15 years / $10,000
- Criminal charges for incest vary by state and on a case-by-case basis: (NOLO, n.d.)29
- Incestual activity toward a child is considered a forcible sex act in all states and a form of child sexual abuse. Perpetrators can also be charged with sexual battery and/or assault.
- Incest between adults is a felony, punishable by prison time and/or a fine. Incest against children is typically punished with lengthy prison terms.
- People convicted of incest will likely have to register as sex offenders, especially if any crimes were committed against children.
The Genetic and Psychological Harm of Incest
Incest is illegal for several reasons. First, inbreeding deals immense harm to the health of inbred children, and victims of incestual abuse suffer a psychological gauntlet of post-traumatic side effects.
Here are the most prevalent ways that incest causes harm:
- Inbreeding leads to congenital disorders, death, physical disabilities, and developmental issues. These problems are directly caused by incest. (Thought Nova, 2022)30
- The closer the two parents are related, the more likely their children will experience negative genetic defects. (Thought Nova, 2022)30
- Sibling sexual abuse is often trivialized as normal sexual exploration but has been linked to psychosocial or psychosexual dysfunction. (Journal of Child Sexual Abuse, 2011)31
- Women who experienced sexual abuse as a child have, on average, 16% higher annual health costs. (Clinical Psychology Review, 2015)27
- Victims of incest can experience the following psychological symptoms: (Patient, 2022)1
- Deliberate self-harm
- Sleep disorders
- Aggressive behavior
- Post-traumatic stress disorder
- Poor concentration
- Poor performance at school
- Eating disorders
- Precocious sexual behavior with peers
Incest, even when consensual, is not a victimless crime. It’s impossible to talk about incest without tearing up over the epidemic of child sexual abuse because most of the sexual abuse of children is incestual.
While the prevalence of incest varies around the world, the numbers often rely on victims who are willing to self-report and perpetrators who were caught in the act. Because of this, incest may be far more common than we know.
The risk of incestual child abuse increases when parents fight or are distant from their children. Abused or neglected children can inflict sexual abuse on their siblings. Parents, aunts, uncles, and grandparents also commonly commit incest on children for a variety of reasons.
First and second-cousin marriages are a common form of consensual incest throughout the world but greatly increase the risk of hereditary diseases and other negative health factors for their children.
Ultimately, incest is linked to abuse and unhealthy sexual attitudes in most of the people who engage in it. More often than not, it is nonconsensual. Whatever the cause of incest may be in any given scenario, it is always preferable to sleep with someone outside your own family.
- Patient, 2022. A medically-reviewed article written by Dr. Hayley Willacy on the medical implications of family sexual abuse.
- RAINN (Rape, Abuse, & Incest National Network), 2009. An article on the definition of incest and the difficulties of reporting sexual abuse by a family member.
- Feminist, 1998. An article on incest as a form of child sexual abuse, specifically toward young adult women.
- Zeitschrift fur klinische Psychologie, Psychopathologie, und Psychotherapie, 1991. A study on the prevalence of child sexual abuse and its long-term effects on victims.
- Medical Science Monitor, 2014. A medical study of 43 cases of incest in 36 females and 7 males aged 4 to 40 conducted at a university in Turkey.
- Child Abuse & Neglect, 2006. A study of sexual abuse among 1,955 female high school students in Istanbul, Turkey.
- Frontiers in Psychiatry, 2022. An article on the prevalence of sibling sexual abuse (SSA) using data from three case reports of adolescent girls and a variety of other studies.
- Evolutionary Psychology, 2019. A study of 632 fathers with daughters from the U.S. and Canada to determine common levels of disgust toward incest and how it affects frequency.
- Child Maltreatment, 2011. A study of childhood sexual abuse reports across 217 publications from 1980 to 2008 with a total of 9,911,748 participants.
- Now Grenada, 2020. An article on the rise of incest during the Covid-19 pandemic in the island nation of Grenada.
- Archives of Sexual Behavior, 2001. A Swedish study of 203 cases of child sexual abuse conducted regionally from 1993 to 1997.
- History of Yesterday, 2021. An article on the origin of human incest and how it has come to be more prevalent today than in the past.
- Nature Communications, 2021. A study of how closely-related parents are today and have been throughout history.
- The Journal of Sex Research, 1982. A study on sibling incest in the royal families of ancient Egypt, Peru, and Hawaii.
- Sexual Life in Ancient China: A Preliminary Survey of Chinese Sex and Society from ca. 1500 B.C. till 1644 A.D, 1974. A book written by Robert Hans van Gulik.
- Oxford University Press, 1983. Life in Egypt Under Roman Rule.
- Hellenic World Encyclopaedia, 2006. An article mentioning Greek law allowing marriage between a brother and sister if they had different mothers.
- Psychiatric Times, 2011. An article on the long-term effects of incest on its victims and the various options for treatment.
- U.S. Department of Justice, 1986. A study sanctioned by the U.S. Department of Justice on the 930 randomly-selected women in San Franciso on the prevalence and effects of incest.
- Medium, 2020. An article on the prevalence of incest in the U.S. and its ramifications for the victims.
- Journal of Spiritual Formation & Soul Care, 2009. An article on the epidemic of child sexual abuse in the U.S. and the incredible damage it does to children.
- Rutgers School of Social Work, 2014. Working with Survivors of Child Incestuous Abuse.
- Psychology Today, 1993. A medically-reviewed article on adult sibling rivalry.
- Child Abuse & Neglect, 1999. An article on the characteristics and consequences of brother-sister incest versus father-daughter incest using data from a survey of 62 female incest survivors.
- Paediatrics and Child Health, 2008. Consanguinity and child health.
- Postgraduate Medicine, 1998. A medical article on defining incest, identifying its trends, and measures to stop instances of incest.
- Clinical Psychology Review, 2015. A meta-analysis on child sexual abuse that compares 6,605 incestual and 10,573 non-incestual offenders as well as analyzes their victims.
- World Population Review, 2022. An infographic report on laws regulating incestual activity in the U.S. by state.
- NOLO, n.d. An article on the various laws and criminal charges associated with incestual activity.
- Thought Nova, 2022. An article on the prevalence of incestual behavior between siblings and its effects.
- Journal of Child Sexual Abuse, 2011. A study on sibling sexual abuse that utilized data from 8 years of National Incident-Based Reporting System (NIBRS) input.