Squamous Intraepithelial Lesion (SIL)

A squamous intraepithelial lesion (SIL) is an area of abnormal tissue on the skin inside of your body. It can affect the cervix, vagina, vulva, anus, penis or back of the throat. These lesions are precancers, which means they’re not cancer but have the potential to become cancer and spread to other tissues.


What is a squamous intraepithelial lesion?

A squamous intraepithelial lesion (SIL) is an area or spot of skin on the inside or outside of your body that grows in a more disorganized way than the skin around it. These areas of skin can form on the lining of certain body parts, like your cervix, vagina, vulva, anus, penis and the back of your throat.

Skin that develops lesions found to be an SIL is usually the result of a virus called the human papillomavirus, or HPV. The skin changes (SIL) themselves cannot be spread from person to person, but the virus can be transmitted through sex as a sexually transmitted infection (STI).

Usually, SILs can be considered “precancers.” This means they aren’t cancer, but they could become cancer if the abnormal cells grow into deeper layers of tissue. SILs can also be called “dysplasia” or “neoplasia”.


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Low-grade vs. high-grade squamous intraepithelial lesion: What’s the difference?

Healthcare providers classify SILs as low-grade or high-grade:

  • Low-grade: Also called mild dysplasia, these lesions only look slightly different under a microscope compared to normal skin. They usually go away on their own without treatment and are less likely to turn into cancer.
  • High-grade: High-grade SILs include moderate dysplasia, severe dysplasia and neoplasia in-situ (the last phase before tissue becomes cancerous). These lesions look very abnormal under a microscope. They usually need some form of treatment right away or they could turn into cancer.

Who’s at risk for squamous intraepithelial lesions?

You’re at an increased risk for SIL if you:

  • Have a suppressed immune system and HPV infection, which make it harder for your body to eliminate abnormal cells caused by the virus.
  • Are a smoker and have HPV, as the chemicals in tobacco increase your risk of cell damage and affect your immune system.
  • In both males and females, anything that increases the risk of HPV infection increases the risk of SIL, including having multiple sexual partners (vaginal, anal or oral sex) and unprotected sex.
  • Older people who had HPV infection during their teenage years or early adulthood.


How common are squamous intraepithelial lesions?

Squamous intraepithelial lesions are common. For instance, healthcare providers diagnose around 200,000 women with cervical dysplasia (SIL) each year. Approximately, 14,000 women will develop cervical cancer due to HPV.

The most common HPV-related cancer in men is oropharyngeal cancer, which is in the back of the throat. It affects about 11,800 men each year.

An HPV vaccine can prevent up to 90% of HPV-related SILs and cancers.

Symptoms and Causes

What causes squamous intraepithelial lesions?

Human papilloma virus (HPV) is a sexually transmitted infection (STI) that causes SIL. There are over 100 different types of HPV infections, but dysplasia that can lead to cancer is usually the result of types 6, 11, 16 and 18. Newer high-risk strains are types 31, 33, 45, 52 and 58.

Repeated HPV infections or infections that last in your body for a long time cause damage to cells. In some people, the cells turn cancerous.


What are the symptoms of squamous intraepithelial lesions?

An SIL doesn’t usually cause symptoms. Most people find out they have it after an exam at their doctor’s office.

Let your healthcare provider know right away if you notice any of the following symptoms in your genitals:

Precancer in the back of your throat may cause:

Diagnosis and Tests

How are squamous intraepithelial lesions diagnosed?

There are a variety of tests that can screen for and diagnose SILs:

It’s important to note that SIL and cancer can take many years after an HPV infection to develop.

Is there routine screening for squamous intraepithelial lesions?

Out of all the HPV-related cancers, routine screening is only recommended for cervical cancer. The U.S. Preventive Services Task Force recommends routine cervical cancer screening for women aged 21 to 65. Based on your age, screening may include a Pap smear, an HPV test or both.

Talk to your healthcare provider about the right screening guidelines for your age and risk level. You may need more frequent screenings if you’ve tested positive for HPV or had abnormal Pap smears in the past.

Management and Treatment

How are squamous intraepithelial lesions treated?

Most low-grade lesions go away on their own. High-grade lesions require immediate treatment. Depending on the location of the lesions, your healthcare provider may recommend:

  • Topical treatments: You may apply some medicine directly to your skin. The creams or ointments may contain chemotherapy, hormones or substances to stimulate your immune system.
  • Cryotherapy: Extreme cold, achieved with liquid nitrogen, can treat some lesions, such as anal or genital warts. Cryotherapy freezes away abnormal tissue.
  • Laser treatment: A powerful laser uses light to burn away abnormal tissue.
  • Excisional surgery: Your healthcare provider may recommend cutting the abnormal tissue out of your body. For cervical dysplasia, you may need a loop electrosurgical excision procedure (LEEP) or a cold knife cone (CKC) excision.


How can I prevent squamous intraepithelial lesions?

The best way to prevent squamous intraepithelial lesions is by getting the HPV vaccine. Girls and boys ages 9 to 14 can get the HPV vaccine series, which is two or three shots spaced two to 12 months apart. If you get the vaccine when you’re older, between ages 15 and 45, you’ll need three doses. If you’re older than 46, talk to your healthcare provider before getting the HPV vaccine.

Other ways to reduce your risk of HPV include:

  • Avoid genital contact with another person whenever possible.
  • Stick to the screening guidelines that are right for your age and risk level.
  • Use condoms and dental dams.

Outlook / Prognosis

What’s the prognosis (outlook) for people with squamous intraepithelial lesions?

Mild (low-grade) SIL usually goes away on its own. Moderate to severe (high-grade) SIL that’s treated early usually doesn’t turn into invasive cancer.

Living With

What questions should I ask my doctor about squamous intraepithelial lesions?

Questions you might want to ask your healthcare provider include:

  • Can an SIL affect my fertility?
  • I can’t remember if I received the HPV vaccine — should I get it now?
  • If I have SIL and haven’t been vaccinated for HPV, should I get the vaccine?
  • If I have HPV but a normal pap, should I get the HPV vaccine anyway?
  • If I have an SIL, what are the chances of it turning into cancer?
  • My Pap test was abnormal — should I worry?
  • What’s my risk of developing an SIL?

When should I contact my doctor?

Contact your healthcare provider if you notice any abnormal symptoms in your genitals, mouth or throat. You should also talk to your healthcare provider if you think you may have had genital contact with someone who has HPV.

A note from Cleveland Clinic

Squamous intraepithelial lesions (SILs) are areas of abnormal tissue that may become cancerous. They’re usually the result of HPV but might not develop until long after you get the infection. SILs typically affect your cervix, vagina, vulva, anus, penis or back of your throat. Some SILs go away on their own, but others need immediate treatment to remove the abnormal tissue before cancer develops.

Medically Reviewed

Last reviewed on 10/26/2021.

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