Consumer DNA tests uncover hidden epidemic of incest

By Todd Neale | Fact-checked by Hale Goetz

Published June 10, 2024

Key Takeaways

The rising popularity of consumer DNA testing has revealed incest is much more common than previously believed.
Research on incest has been stifled in recent decades, potentially due to widespread backlash against therapists for suggesting abuse that hadn’t actually occurred.
When patients report a history of incest and ask for guidance, you can share information about evidence-based psychotherapeutic approaches and support groups that can help them heal.

Many consumers turn to mail-order DNA testing companies (such as 23andMe) to learn about their ancestry—an increasingly popular practice.

However, these tests have also revealed a surprising finding: Incest appears to be much more common than previously believed.

This has implications not only for those who have been affected by incest, but also for the clinicians who treat the physical and mental scars left behind.

The prevalence of incest

Solid numbers on the prevalence of incest are hard to come by due to the stigma attached to it and the difficulty in getting people to talk about it.

One widely cited figure, dating back to a 1975 psychiatry textbook, puts the prevalence of father-daughter incest at 1 in every 1 million families in the US—a number that has since been found to be a gross underestimate.^[]

The rise of consumer DNA testing services has proved that incest is not just a one-in-a-million kind of thing. According to a recent article in The Atlantic, unpublished research from UK Biobank (a large, anonymized research database) showed 1 in every 7,000 participants was born to parents who were first-degree relatives—either siblings, or a parent and a child.^[]

Considering that not all cases of incest will result in pregnancy, the true prevalence of incest is likely even higher.

Mental and physical impacts

Unfortunately, research on incest and its effects has been stifled in recent decades, a phenomenon a psychiatrist writing in Psychiatric Times suggests could be related to a movement starting in the early 1990s accusing therapists of suggesting abuse that hadn’t actually occurred.^[]

Still, there is evidence that incest carries potential harm to both physical and mental health, which takes on greater importance amid higher-than-expected estimates of the problem.

The Rape, Abuse & Incest National Network (RAINN), the largest anti-sexual violence organization in the US, lists a host of health problems that can impact people who have experienced sexual violence, including incest.^[] These include depression, flashbacks, self-harm, STIs, substance abuse, dissociation, panic attacks, eating disorders, unwanted pregnancies, sleep disorders, and suicide.

Survivors may also suffer from post-traumatic stress disorder, which in turn has been linked to sexual dysfunction, particularly among military veterans and survivors of childhood sexual abuse.

Another organization, Incest AWARE, lists additional health issues that can arise following incest, such as lingering feelings of being alone or unloved, low self-esteem, and chronic physical pain or illness, among others.^[]

Importantly, if a child is conceived after two closely related family members have sex, there is a heightened risk of him or her having a recessive genetic disorder that increases the risk of neonatal mortality, negatively impacts intellectual abilities, or causes developmental disorders, cystic fibrosis, premature birth, cleft palate, or heart problems.^[]

Preventing 'accidental incest'

The greater prevalence of incest also raises concerns about “inadvertent consanguineous conception,”^[] or accidental incest, that can occur when two individuals conceived using sperm from the same donor later have a child together.

Fertility clinics generally limit the number of times a donor’s sperm can be used to mitigate this worry, and the issue is also addressed in current guidelines on gamete and embryo donation from the American Society for Reproductive Medicine.^[] The group recommends maintaining sufficient records to set a limit on the number of pregnancies that can be achieved with a given donor’s sperm, with considerations for the population and geographic area the donor comes from.

Though efforts are being made to limit accidental incest, systems around the world are not foolproof: CNN reported last year that a Dutch man was ordered by a court to stop donating sperm after fathering 500 to 600 children around the world.^[]

Treatment for those affected

Treatments are, fortunately, available to help anyone who has been harmed by incest. Authors publishing in Innovations in Clinical Neuroscience reviewed psychotherapy options for survivors of sexual abuse and assault in general, but this would apply to those with a history of incest as well.^[] Evidence-based treatments include psychodynamic psychotherapy, trauma-focused cognitive behavioral therapy, and eye movement desensitization and reprocessing therapy.

"Processing abuse and trauma is a helpful and necessary step to recovery and is the main focus in these treatment modalities."

— Authors, Innovations in Clinical Neuroscience

The authors also emphasized the need to avoid re-traumatization during therapy. But, aside from formal therapy, support groups are also available to help individuals who need it, providing another avenue to recommend for your patients. RAINN operates the National Sexual Assault Online Hotline. Additionally, a group called Surivors of Incest Anonymous provides resources to those with a history of childhood sexual abuse.

What this means for you

The rise of mail-order DNA testing for genetic genealogy has revealed incest is more prevalent than prior estimates. This means that the physical and mental health effects in survivors may be a greater problem than is currently appreciated. You can tell your patients who have been impacted by incest that psychotherapeutic approaches have been shown to have benefits, and that there are support groups available to help.