Causes and Risk Factors of Cervical Intraepithelial Neoplasia (CIN)

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Cervical intraepithelial neoplasia (CIN) is caused by human papillomavirus (HPV) infecting a woman’s reproductive tract and leading to abnormal cell growth (lesioning) on the outer lining of the cervix.

These non-cancerous lesions are formally referred to as low-grade or high-grade squamous intraepithelial lesions, depending on the seriousness of the changes.

There are more than 100 types of HPV, of which at least 14 are cancer-causing, otherwise categorized as high-risk.

What You Should Know About Cervical Intraepithelial Neoplasia (CIN)

Verywell / Jessica Olah

Common Causes

In most cases, CIN develops after an HPV infection. HPV is a sexually transmitted infection that spreads easily from person to person.

Human Papillomavirus Infection

More than three-quarters of all sexually active women are expected to become infected with HPV at some point in their lifetime.

Not everyone who gets HPV will experience CIN, though. Experts say the immune system is well suited to clearing HPV infections without any external intervention.

However, it’s not exactly clear why some people clear the infection and others develop CIN. It’s thought to be a combination of risk factors that can help predict your likelihood of CIN.

CIN is usually caused by HPV, a sexually transmitted infection. This doesn’t mean engaging in sexual activity “causes” CIN, though. Instead, it would be considered a risk factor for CIN. If you ever get an abnormal pap test result, your doctor will consider your risk factors to determine your likelihood of HPV potentially progressing to cervical cancer.

Genetics

Certain gene variations have been linked to CIN and cervical cancer. An analysis conducted in 2019 on gene mutations in patients with CIN and patients with cervical cancer detected gene mutations in 52% of the CIN specimens, and 54.8% of these mutations occurred in genes that also mutated in cervical cancers.

Mutated Genes in Cervical Cancer

Mutated genes found in cervical cancer include four genes:

  • FAT1
  • MLL3
  • MLL2 
  • FADD

High-Risk HPV Strains

Importantly, high-risk HPV strains in cervical cancers were similarly found in CIN samples. High-risk HPV strains include:

  • HPV16
  • HPV18
  • HPV33 
  • HPV58

Risk Factors

Risk factors aren’t considered causes in the same sense that they’re the “reason” why someone develops a certain disease. Rather, risk factors demonstrate your personal risk of developing CIN or HPV based upon specific factors other than genetics. 

Age

A 2019 age-specific risk assessment looked at 9,434 women with HPV-pap co-testing. Follow-up cervical biopsy found:

  • The highest risk was noted among women under 40 years of age.
  • The lowest risk was observed in women ages 50 to 59 years.
  • Women under 30 years were found to have a similar risk profile to those of women ages 30 to 39 years.

About 50% of HPV infections occur in girls and women between the ages of 15 and 25.

HIV-Positive Status

The human immunodeficiency virus, HIV, is the virus that can lead to AIDS.

The likelihood that a woman living with HIV will develop invasive cervical cancer is up to five times higher than for a woman who is not living with HIV. This is according to UNAIDS, an organization dedicated to leading the global effort to end AIDS as a public health threat by 2030.

Becoming infected with HIV is known as a risk factor for CIN because it weakens your immune system. A compromised immune system will have more difficulty fighting off any HPV infections that could then develop into CIN.

Taking Immunosuppressants

Some conditions, like rheumatoid arthritis or psoriatic arthritis, or medical events like organ transplantation, also affect the immune system. In these cases, your immune system may be overreacting and actually attacking healthy cells.

You may be prescribed immunosuppressant medications (oral, injectable, or topical) to calm this process and slow any joint damage, but this also weakens your defenses against other infections, like HPV and HPV-associated disease.

Lifestyle Factors

Lifestyle factors are factors that—with the right support—you have the power to change. The following have all been identified as potential lifestyle factors that contribute to your susceptibility or vulnerability of developing HPV or CIN.

Smoking Cigarettes

The American Cancer Society says that women who smoke are about twice as likely as those who don’t smoke to get cervical cancer. 

According to the ACS, researchers believe the toxic substances in tobacco damage the DNA of cervix cells and may contribute to the development of cervical cancer. Smoking is also known to weaken the immune system, making it less effective at fighting HPV infections.

Sexual Activities 

The reason why certain sexual activities are considered lifestyle risk factors is most likely because they increase the chances of exposure to HPV.

Examples include:

  • Becoming sexually active at younger than 18 years old
  • Having multiple sexual partners (although HPV can be transmitted in a single sexual interaction)
  • Having any one partner who is considered high risk (someone with HPV infection or who has many sexual partners)

Socioeconomic Status

Not having easy or affordable access to health care, including cervical cancer screening with pap tests and HPV tests, can create a very real barrier to people getting screened and detecting CIN in its earlier stages. Without these tests, it’s not possible to know whether or not you have CIN or HPV that can lead to cervical cancer.

A Word From Verywell

While the main cause of CIN is HPV infection, CIN itself is not a sexually transmitted disease. There are many other risk factors and lifestyle factors that can contribute to your chances of developing abnormal cell growth on your cervix.

You can protect yourself by working to change your lifestyle factors. This includes making sure you always practice safe sex.

If you do develop CIN from HPV, it’s important to know that it’s not your fault. Some people’s immune systems will destroy the issue, and others will not. Talk to your doctor if you have concerns about your own risk factors.

Frequently Asked Questions

  • Are HPV and CIN the same?

    No, HPV (human papillomavirus) causes an infection that can lead to CIN, but they are not the same.

  • Can you have CIN without HPV?

    Yes, it is possible for your doctor to detect abnormal cell growth or lesions even when you don’t have HPV. However, the majority (90%) of cases of CIN are caused by HPV infection.

  • Can you prevent CIN?

    While you can’t exactly prevent CIN, you can see if you’re eligible for the HPV vaccine, which helps prevent against HPV. The CDC recommends HPV vaccination for all boys and girls at ages 11-12 to protect against HPV-related infections and cancers.

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8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Cleveland Clinic. Cervical intraepithelial neoplasia (CIN). Updated May 7, 2014.

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